In October 1860, Bernhard Mahler moved with his wife and infant son, Gustav, to the town of Iglau (Jihlava), 25 km (16 mi) to the southeast (Moravia), where he built up a distillery and tavern Business. The family grew rapidly, but of the 12 children (only 3 daughters) born to the family in Iglau only six survived infancy. Iglau was then a thriving commercial town of 20,000 people where Gustav was introduced to music through street songs, dance tunes, folk melodies, and the trumpet calls and marches of the local military band. All of these elements would later contribute to his mature musical vocabulary.

Bernhard Mahler supported his son's ambitions for a music career, and agreed that the boy should try for a place at the Vienna Conservatory. The young Mahler was auditioned by the renowned Pianist Julius Epstein, and accepted for 1875–76. He made good progress in his piano studies with Epstein and won prizes at the end of each of his first two years. For his final year, 1877–78, he concentrated on composition and harmony under Robert Fuchs and Franz Krenn. Few of Mahler's student compositions have survived; most were abandoned when he became dissatisfied with them. He destroyed a symphonic movement prepared for an end-of-term competition, after its scornful rejection by the autocratic Director Joseph Hellmesberger on the grounds of copying errors. Mahler may have gained his first conducting experience with the Conservatory's student orchestra, in rehearsals and performances, although it appears that his main role in this orchestra was as a percussionist.

As he waited for the Emperor's confirmation of his directorship, Mahler shared duties as a resident Conductor with Joseph Hellmesberger Jr. (son of the former conservatory director) and Hans Richter, an internationally renowned interpreter of Wagner and the Conductor of the original Ring cycle at Bayreuth in 1876. Director Wilhelm Jahn had not consulted Richter about Mahler's appointment; Mahler, sensitive to the situation, wrote Richter a complimentary letter expressing unswerving admiration for the older Conductor. Subsequently, the two were rarely in agreement, but kept their divisions private.

Among Mahler's fellow students at the Conservatory was the Future song Composer Hugo Wolf, with whom he formed a close friendship. Wolf was unable to submit to the strict disciplines of the Conservatory and was expelled. Mahler, while sometimes rebellious, avoided the same fate only by writing a penitent letter to Hellmesberger. He attended occasional lectures by Anton Bruckner and, though never formally his pupil, was influenced by him. On 16 December 1877, he attended the disastrous premiere of Bruckner's Third Symphony, at which the Composer was shouted down, and most of the audience walked out. Mahler and other sympathetic students later prepared a piano version of the symphony, which they presented to Bruckner. Along with many music students of his generation, Mahler fell under the spell of Richard Wagner, though his chief interest was the sound of the music rather than the staging. It is not known whether he saw any of Wagner's operas during his student years.

Mahler left the Conservatory in 1878 with a diploma but without the silver medal given for outstanding achievement. He then enrolled in the University of Vienna (he had, at his father's insistence, sat and with difficulty passed the "matura," or entrance examination) and followed courses which reflected his developing interests in literature and philosophy. After leaving the University in 1879, Mahler made some money as a piano Teacher, continued to compose, and in 1880 finished a dramatic cantata, Das klagende Lied ("The Song of Lamentation"). This, his first substantial composition, shows traces of Wagnerian and Brucknerian influences, yet includes many musical elements which musicologist Deryck Cooke describes as "pure Mahler." Its first performance was delayed until 1901, when it was presented in a revised, shortened form.

Deryck Cooke and other analysts have divided Mahler's composing life into three distinct phases: a long "first period," extending from Das klagende Lied in 1880 to the end of the Wunderhorn phase in 1901; a "middle period" of more concentrated composition ending with Mahler's departure for New York in 1907; and a brief "late period" of elegiac works before his death in 1911.

From the beginning of January 1883, Mahler became Conductor at the Royal Municipal Theatre in Olmütz (now Olomouc) in Moravia. He later wrote: "From the moment I crossed the threshold of the Olmütz theatre I felt like one awaiting the wrath of God." Despite poor relations with the orchestra, Mahler brought nine (13 times) operas to the theatre, including the new Bizet's Carmen, and won over the press that had initially been sceptical to him. After a week's trial at the Royal Theatre in the Hessian town of Kassel, Mahler became the theatre's "Musical and Choral Director" from August 1883. The title concealed the reality that Mahler was subordinate to the theatre's Kapellmeister, Wilhelm Treiber, who disliked him (and vice-versa) and set out to make his life miserable. Despite the unpleasant atmosphere, Mahler had moments of success at Kassel. He directed a performance of his favourite opera, Weber's Der Freischütz, and 25 other operas. On 23 June 1884, he conducted his own incidental music to Joseph Victor von Scheffel's play Der Trompeter von Säckingen ("The Trumpeter of Säckingen"), the first professional public performance of a Mahler work. An ardent, but ultimately unfulfilled, love affair with Soprano Johanna Richter led Mahler to write a series of love poems which became the text of his song cycle Lieder eines fahrenden Gesellen ("Songs of a Wayfarer").

In January 1884, the distinguished Conductor Hans von Bülow brought the Meiningen Court Orchestra to Kassel and gave two concerts. Hoping to escape from his job in the theatre, Mahler unsuccessfully sought a post as Bülow's permanent assistant. However, in the following year his efforts to find new employment resulted in a six-year contract with the prestigious Leipzig Opera, to begin in August 1886. Unwilling to remain in Kassel for another year, Mahler resigned on 22 June 1885, and applied for, and through good fortune was offered a standby appointment as Conductor at the Royal Deutsches Landestheater in Prague by the theatre's newly appointed Director, the famous Angelo Neumann.

In Prague, the emergence of Czech National Revival had increased the popularity and importance of the new Czech National Theatre, and had led to a downturn in the Royal Landstheater fortunes. Mahler's task was to help arrest this decline by offering high-quality productions of German opera. He enjoyed early success presenting works by Mozart and Wagner, composers with whom he would be particularly associated for the rest of his career, but his individualistic and increasingly autocratic conducting style led to friction, and a falling out with his more experienced fellow-conductor, Ludwig Slansky. During his 12 months in Prague he conducted 68 performances of 14 operas (12 titles were new in his repertory), and he also performed Beethoven's Ninth for the first time in his life. By the end of the season, in July 1886, Mahler left Prague to take up his post at the Neues Stadttheater in Leipzig, where rivalry with his senior colleague Arthur Nikisch almost began at once. This conflict was primarily over how the two should share conducting duties for the theatre's new production of Wagner's Ring cycle. Nikisch's illness, from February to April 1887, meant that Mahler took charge of the whole cycle (except Götterdämmerung), and scored a resounding public success. This did not, however, win him popularity with the orchestra, who resented his dictatorial manner and heavy rehearsal schedules.

In the early years of Mahler's conducting career, composing was a spare time activity. Between his Laibach and Olmütz appointments he worked on settings of verses by Richard Leander and Tirso de Molina, later collected as Volume I of Lieder und Gesänge ("Songs and Airs"). Mahler's first orchestral song cycle, Lieder eines fahrenden Gesellen, composed at Kassel, was based on his own verses, although the first poem, "Wenn mein Schatz Hochzeit macht" ("When my love becomes a bride") closely follows the text of a Wunderhorn poem. The melodies for the second and fourth songs of the cycle were incorporated into the First Symphony, which Mahler finished in 1888, at the height of his relationship with Marion von Weber. The intensity of Mahler's feelings are reflected in the music, which originally was written as a five-movement symphonic poem with a descriptive programme. One of these movements, the "Blumine," later discarded, was based on a passage from his earlier work Der Trompeter von Säckingen. After completing the symphony, Mahler composed a 20-minute symphonic poem, Totenfeier "Funeral Rites", which later became the first movement of his Second Symphony.

On 18 February 1889, Bernhard Mahler died; this was followed later in the year by the deaths both of Mahler's sister Leopoldine (27 September) and his mother (11 October). From October 1889 Mahler took charge of his four younger brothers and sisters (Alois, Otto, Justine, and Emma). They were installed in a rented flat in Vienna. Mahler himself suffered poor health, with attacks of haemorrhoids and migraine and a recurrent septic throat. Shortly after these family and health setbacks the premiere of the First Symphony, in Budapest on 20 November 1889, was a disappointment. The critic August Beer's lengthy newspaper review indicates that enthusiasm after the early movements degenerated into "audible opposition" after the Finale. Mahler was particularly distressed by the negative comments from his Vienna Conservatory contemporary, Viktor von Herzfeld, who had remarked that Mahler, like many conductors before him, had proved not to be a Composer.

On arriving in Budapest in October 1888, Mahler encountered a cultural conflict between conservative Hungarian nationalists who favoured a policy of Magyarisation, and progressives who wanted to maintain and develop the country's Austro-German cultural traditions. In the opera house a dominant conservative caucus, led by the music Director Sándor Erkel, had maintained a limited repertory of historical and folklore opera. By the time that Mahler began his duties, the progressive camp had gained ascendancy following the appointment of the liberal-minded Ferenc von Beniczky as intendant. Aware of the delicate situation, Mahler moved cautiously; he delayed his first appearance on the conductor's stand until January 1889, when he conducted Hungarian-language performances of Das Rheingold and Die Walküre to initial public acclaim. However, his early successes faded when plans to stage the remainder of the Ring cycle and other German operas were frustrated by a renascent conservative faction which favoured a more traditional "Hungarian" programme. In search of non-German operas to extend the repertory, Mahler visited in spring 1890 Italy where among the works he discovered was Pietro Mascagni's recent sensation Cavalleria rusticana (Budapest premiere on 26 December 1890).

In 1891, Hungary's move to the political right was reflected in the opera house when Beniczky on 1 February was replaced as intendant by Count Géza Zichy, a conservative aristocrat determined to assume artistic control over Mahler's head. However, Mahler had foreseen that and had secretly been negotiating with Bernhard Pollini, the Director of the Stadttheater Hamburg since summer and autumn of 1890, and a contract was finally signed in secrecy on 15 January 1891. Mahler more or less "forced" himself to be sacked from his Budapest post, and he succeeded on 14 March 1891. By his departure he received a large sum of indemnity. One of his final Budapest triumphs was a performance of Don Giovanni (16 September 1890) which won him praise from Brahms, who was present at the performances on 16 December 1890. During his Budapest years Mahler's compositional output had been limited to a few songs from the Wunderhorn song settings that became Volumes II and III of Lieder und Gesänge, and amendments to the First Symphony.

Except for his juvenilia, little of which has survived, Mahler composed only in the media of song and symphony, with a close and complex interrelationship between the two. Donald Mitchell writes that this interaction is the backcloth against which all Mahler's music can be considered. The initial connection between song and symphony occurs with the song-cycle Lieder eines fahrenden Gesellen and the First Symphony. Although this early evidence of cross-fertilisation is important, it is during Mahler's extended Wunderhorn phase, in which his Second, Third and Fourth Symphonies were written, that the song and symphony genres are consistently intermingled. Themes from the Wunderhorn song Das himmlische Leben ("The Heavenly Life"), composed in 1892, became a key element in the Third Symphony completed in 1896; the song itself forms the finale to the Fourth (1900) and its melody is central to the whole composition. For the Second Symphony, written between 1888 and 1894, Mahler worked simultaneously on the Wunderhorn song, Des Antonius von Padua Fischpredigt ("The Sermon of St Anthony of Padua to the Fishes"), and on the Scherzo based on it which became the symphony's third movement. Another Wunderhorn setting from 1892, Urlicht ("Primal Light"), is used as the Second Symphony's fourth (penultimate) movement.

Performances of Mahler works were still comparatively rare (he had not composed very much). On 27 October 1893, at Hamburg's Konzerthaus Ludwig, Mahler conducted a revised version of his First Symphony; still in its original five-movement form, it was presented as a Tondichtung (tone poem) under the descriptive name "Titan". This concert also introduced six recent Wunderhorn settings. Mahler achieved his first relative success as a Composer when the Second Symphony was well-received on its premiere in Berlin, under his own baton, on 13 December 1895. Mahler's conducting assistant Bruno Walter, who was present, said that "one may date [Mahler's] rise to fame as a Composer from that day." That same year Mahler's private life had been disrupted by the suicide of his younger brother Otto on 6 February.

Mahler's Hamburg post was as chief Conductor, subordinate to the Director, Bernhard Pohl (known as Pollini) who retained overall artistic control. Pollini was prepared to give Mahler considerable leeway if the Conductor could provide commercial as well as artistic success. This Mahler did in his first season, when he conducted Wagner's Tristan und Isolde for the first time and gave acclaimed performances of the same composer's Tannhäuser and Siegfried. Another triumph was the German premiere of Tchaikovsky's Eugene Onegin, in the presence of the Composer, who called Mahler's conducting "astounding," and later asserted in a letter that he believed Mahler was "positively a genius." Mahler's demanding rehearsal schedules led to predictable resentment from the Singers and orchestra with whom, according to music Writer Peter Franklin, the Conductor "inspired hatred and respect in almost equal measure." He found support, however, from Hans von Bülow, who was in Hamburg as Director of the city's subscription concerts. Bülow, who had spurned Mahler's approaches in Kassel, had come to admire the younger man's conducting style, and on Bülow's death in 1894 Mahler took over the direction of the concerts.

At the Stadttheater Mahler's repertory consisted of 66 operas of which 36 titles were new to him. During his six years in Hamburg he conducted 744 performances, amongst other he introduced: Verdi's Falstaff, Humperdinck's Hänsel und Gretel, and works by Smetana. However, he was forced to resign his post with the subscription concerts after poor financial returns and an ill-received interpretation of his re-scored Beethoven's Ninth Symphony. Already at an early age Mahler had made it clear that his ultimate goal was an appointment in Vienna, and from 1895 onward was manoeuvring, with the help of influential friends, to secure the directorship of the Vienna Hofoper. He overcame the bar that existed against the appointment of a Jew to this post by what may have been a pragmatic conversion to Roman Catholicism in February 1897. Despite this event, Mahler has been described as a lifelong agnostic.

Vienna, the imperial Habsburg capital, had recently elected an anti-Semitic conservative mayor, Karl Lueger, who had once proclaimed: "I myself decide who is a Jew and who isn't." In such a volatile political atmosphere Mahler needed an early demonstration of his German cultural credentials. He made his initial mark in May 1897 with much-praised performances of Wagner's Lohengrin and Mozart's Die Zauberflöte. Shortly after the Zauberflöte triumph, Mahler was forced to take sick leave for several weeks, during which he was nursed by his sister Justine and his long-time companion, the viola player Natalie Bauer-Lechner. Mahler returned to Vienna in late July to prepare for Vienna's first uncut version of the Ring cycle. This performance took place on 24–27 August, attracting critical praise and public enthusiasm. Mahler's friend Hugo Wolf told Bauer-Lechner that "for the first time I have heard the Ring as I have always dreamed of hearing it while reading the score."

When Richter resigned as head of the Vienna Philharmonic subscription concerts in September 1898, the concerts committee had unanimously chosen Mahler as his successor. The appointment was not universally welcomed; the anti-Semitic press wondered if, as a non-German, Mahler would be capable of defending German music. Attendances rose sharply in Mahler's first season, but members of the orchestra were particularly resentful of his habit of re-scoring acknowledged masterpieces, and of his scheduling of extra rehearsals for works with which they were thoroughly familiar. An attempt by the orchestra to have Richter reinstated for the 1899 season failed, because Richter was not interested. Mahler's position was weakened when, in 1900, he took the orchestra to Paris to play at the Exposition Universelle. The Paris concerts were poorly attended and lost money—Mahler had to borrow the orchestra's fare home from the Rothschilds. In April 1901, dogged by a recurrence of ill-health and wearied by more complaints from the orchestra, Mahler relinquished the Philharmonic concerts conductorship. In his three seasons he had performed around 80 different works, which included pieces by relatively unknown composers such as Hermann Goetz, Wilhelm Kienzl and the Italian Lorenzo Perosi.

The demands of his twin appointments in Vienna initially absorbed all Mahler's time and Energy, but by 1899 he had resumed composing. The remaining Vienna years were to prove particularly fruitful. While working on some of the last of his Des Knaben Wunderhorn settings he started his Fourth Symphony, which he completed in 1900. By this time he had abandoned the composing hut at Steinbach and had acquired another, at Maiernigg on the shores of the Wörthersee in Carinthia, where he later built a villa. In this new venue Mahler embarked upon what is generally considered as his "middle" or post-Wunderhorn compositional period. Between 1901 and 1904 he wrote ten settings of poems by Friedrich Rückert, five of which were collected as Rückert-Lieder. The other five formed the song cycle Kindertotenlieder ("Songs on the Death of Children"). The trilogy of orchestral symphonies, the Fifth, the Sixth and the Seventh were composed at Maiernigg between 1901 and 1905, and the Eighth Symphony written there in 1906, in eight weeks of furious activity.

Within this same period Mahler's works began to be performed with increasing frequency. In April 1899 he conducted the Viennese premiere of his Second Symphony; 17 February 1901 saw the first public performance of his early work Das klagende Lied, in a revised two-part form. Later that year, in November, Mahler conducted the premiere of his Fourth Symphony, in Munich, and was on the rostrum for the first complete performance of the Third Symphony, at the Allgemeiner Deutscher Musikverein festival at Krefeld on 9 June 1902. Mahler "first nights" now became increasingly frequent musical events; he conducted the first performances of the Fifth and Sixth Symphonies at Cologne and Essen respectively, in 1904 and 1906. Four of the Rückert-Lieder, and Kindertotenlieder, were introduced in Vienna on 29 January 1905.

In a letter to Alma dated 16 February 1902, Mahler wrote, with reference to Richard Strauss: "My day will come when his is ended. If only I might live to see it, with you at my side!" Carr observes that Mahler could conceivably have lived to see "his day"; his near-contemporary Richard Strauss survived until 1949, while Sibelius, just five years younger than Mahler, lived until 1957.

Donald Mitchell writes that Mahler's influence on succeeding generations of composers is "a complete subject in itself." Mahler's first disciples included Arnold Schoenberg and his pupils Alban Berg and Anton Webern, who together founded the Second Viennese School. Mahler's music influenced the trio's move from progressive tonalism to atonality (music without a key); although Mahler rejected atonality, he became a fierce defender of the bold originality of Schoenberg's work. At the premiere of the latter's First String Quartet in February 1907, Mahler reportedly was held back from physically attacking the hecklers. Schoenberg's Serenade, Op. 24 (1923), Berg's Three Pieces for Orchestra (1915) and Webern's Six Pieces (1928) all carry echoes of Mahler's Seventh Symphony.

Mahler made his New York debut at the Metropolitan Opera on 1 January 1908, when he conducted Wagner's Tristan und Isolde in the cut version still standard in New York, though long since superseded in Vienna. In a busy first season Mahler's performances were widely praised, especially his Fidelio on 20 March 1908, in which he insisted on using replicas being made of Roller's Vienna sets. On his return to Austria for the summer of 1908, Mahler established himself in the third and last of his composing studios, in the pine forests close to Toblach in Tyrol. Here, using a text by Hans Bethge based on ancient Chinese poems, he composed Das Lied von der Erde ("The Song of the Earth"). Despite the symphonic nature of the work, Mahler refused to number it, hoping thereby to escape the "curse of the Ninth Symphony" that he believed had affected fellow-composers Beethoven, Schubert and Bruckner. On 19 September 1908 the premiere of the Seventh Symphony, in Prague, was deemed by Alma Mahler a critical rather than a popular success.

Back in Europe for the summer of 1909, Mahler worked on his Ninth Symphony and made a conducting tour of the Netherlands. The 1909–10 New York Philharmonic season was long and taxing; Mahler rehearsed and conducted 46 concerts, but his programmes were often too demanding for popular tastes. His own First Symphony, given its American debut on 16 December 1909, was one of the pieces that failed with critics and public, and the season ended with heavy financial losses. The highlight of Mahler's 1910 summer was the first performance of the Eighth Symphony at Munich on 12 September, the last of his works to be premiered in his lifetime. The occasion was a triumph—"easily Mahler's biggest lifetime success," according to biographer Robert Carr—but it was overshadowed by the composer's discovery, before the event, that Alma had begun an affair with the young Architect Walter Gropius. Greatly distressed, Mahler sought advice from Sigmund Freud, and appeared to gain some comfort from his meeting with the psychoanalyst. One of Freud's observations was that much damage had been done by Mahler's insisting that Alma give up her composing. Mahler accepted this, and started to positively encourage her to write music, even editing, orchestrating and promoting some of her works. Alma agreed to remain with Mahler, although the relationship with Gropius continued surreptitiously. In a gesture of love, Mahler dedicated his Eighth Symphony to her.

A mix of enthusiasm, consternation and critical contempt became the normal response to new Mahler symphonies, although the songs were better received. After his Fourth and Fifth Symphonies failed to gain general public approval, Mahler was convinced that his Sixth would finally succeed. However, its reception was dominated by satirical comments on Mahler's unconventional percussion effects—the use of a wooden mallet, birch rods and a huge square bass drum. Viennese critic Heinrich Reinhardt dismissed the symphony as "Brass, lots of brass, incredibly much brass! Even more brass, nothing but brass!" The one unalloyed performance triumph within Mahler's lifetime was the premiere of the Eighth Symphony in Munich, on 12 September 1910, advertised by its promoters as the "Symphony of a Thousand." At its conclusion, applause and celebrations reportedly lasted for half an hour.

Mahler's friend Guido Adler calculated that at the time of the composer's death in 1911 there had been more than 260 performances of the symphonies in Europe, Russia and America, the Fourth Symphony with 61 performances given most frequently (Adler did not enumerate performances of the songs). In his lifetime, Mahler's works and their performances attracted wide interest, but rarely unqualified approval; for years after its 1889 premiere critics and public struggled to understand the First Symphony, described by one critic after an 1898 Dresden performance as "the dullest [symphonic] work the new epoch has produced." The Second Symphony was received more positively, one critic calling it "the most masterly work of its kind since Mendelssohn." Such generous praise was rare, particularly after Mahler's accession to the Vienna Hofoper directorship. His many enemies in the city used the anti-Semitic and conservative press to denigrate almost every performance of a Mahler work; thus the Third Symphony, a success in Krefeld in 1902, was treated in Vienna with critical scorn: "Anyone who has committed such a deed deserves a couple of years in prison."

Performances of Mahler's works became less frequent after his death. In the Netherlands the advocacy of Willem Mengelberg ensured that Mahler remained popular there, and Mengelberg's engagement with the New York Philharmonic from 1922 to 1928 brought Mahler regularly to American audiences. However, much American critical reaction in the 1920s was negative, despite a spirited effort by the young Composer Aaron Copland to present Mahler as a progressive, 30 years ahead of his time and infinitely more inventive than Richard Strauss. Earlier, in 1916, Leopold Stokowski had given the American premieres of the Eighth Symphony and Das Lied von der Erde in Philadelphia. The Eighth was a sensationally successful performance that was immediately taken to New York where it scored a further triumph. An early proponent of Mahler's work in Britain was Adrian Boult, who as Conductor of the City of Birmingham Orchestra performed the Fourth Symphony in 1926 and Das Lied von der Erde in 1930. The Hallé Orchestra brought Das Lied and the Ninth Symphony to Manchester in 1931; Sir Henry Wood staged the Eighth in London in 1930, and again in 1938 when the young Benjamin Britten found the performance "execrable" but was nevertheless impressed by the music. British critics during this period largely treated Mahler with condescension and faint praise. Thus Dyneley Hussey, writing in 1934, thought the "children's songs" were delightful, but that the symphonies should be let go. Composer-conductor Julius Harrison described Mahler's symphonies as "interesting at times, but laboriously put together" and as lacking creative spark. Bernard Shaw, in his role as music critic, thought that the musical audiences of the 1930s would find Mahler (and Bruckner) "expensively second-rate."

Before Mahler's music was banned as "degenerate" during the Nazi era, the symphonies and songs were played in the concert halls of Germany and Austria, often conducted by Bruno Walter or Mahler's younger assistant Otto Klemperer, and also by Willem Mengelberg. In Austria, Mahler's work experienced a brief renaissance between 1934 and 1938, a period known today as 'Austrofascism', when the authoritarian regime with the help of Alma Mahler and Bruno Walter, who were both on friendly terms with the new chancellor Kurt Schuschnigg, sought to make Mahler into a national icon (with a status comparable to that of Wagner in Germany). Mahler's music was performed during the Nazi era in Berlin in early 1941 and in Amsterdam during the German occupation of the Netherlands by Jewish orchestras and for Jewish audiences alone; works performed included the Second Symphony (Berlin), the First and Fourth Symphonies, and the Songs of a Wayfarer (Amsterdam).

There has been frequent speculation about lost or destroyed works from Mahler's early years. The Dutch Conductor Willem Mengelberg believed that the First Symphony was too mature to be a first symphonic work, and must have had predecessors. In 1938, Mengelberg revealed the existence of the so-called "Dresden archive," a series of manuscripts in the possession of the widowed Marion von Weber. According to the Mahler Historian Donald Mitchell, it was highly likely that important Mahler manuscripts of early symphonic works had been held in Dresden; this archive, if it existed, was almost certainly destroyed in the bombing of Dresden in 1945.

On 8 October Mahler was formally appointed to succeed Jahn as the Hofoper's Director. His first production in his new office was Smetana's Czech nationalist opera Dalibor, with a reconstituted finale that left the hero Dalibor alive. This production caused anger among the more extreme Viennese German nationalists, who accused Mahler of "fraternising with the anti-dynastic, inferior Czech nation." The Austrian author Stefan Zweig, in his memoirs The World of Yesterday (1942), described Mahler's appointment as an Example of the Viennese public's general distrust of young artists: "Once, when an amazing exception occurred and Gustav Mahler was named Director of the Court Opera at thirty-eight years old, a frightened murmur and astonishment ran through Vienna, because someone had entrusted the highest institute of art to 'such a young person' ... This suspicion—that all young people were 'not very reliable'—ran through all circles at that time." Zweig also wrote that "to have seen Gustav Mahler on the street [in Vienna] was an event that one would proudly report to his comrades the next morning as it if were a personal triumph." During Mahler's tenure a total of 33 new operas were introduced to the Hofoper; a further 55 were new or totally revamped productions. However, a proposal to stage Richard Strauss's controversial opera Salome in 1905 was rejected by the Viennese censors.

According to American Composer David Schiff, his compatriot Leonard Bernstein used to imply that he had single-handedly rescued Mahler from oblivion in 1960, after 50 years of neglect. Schiff points out that such neglect was only relative—far less than the (incomplete) disregard of Bach in the years after his death. Although Bernstein gave the Mahler revival further impetus, it was well under way before 1960, sustained by conductors such as Stokowski, Dimitri Mitropoulos and John Barbirolli, and by the long-time Mahler advocate Aaron Copland. Mahler himself predicted his place in history, once commenting: "Would that I could perform my symphonies for the first time 50 years after my death!"

Alma Mahler survived her husband by more than 50 years, dying in 1964. She married Walter Gropius in 1915, divorced him five years later, and married the Writer Franz Werfel in 1929. In 1940 she published a memoir of her years with Mahler, entitled Gustav Mahler: Memories and Letters. This account was criticised by later biographers as incomplete, selective and self-serving, and for providing a distorted picture of Mahler's life. The composer's daughter Anna Mahler became a well-known sculptor; she died in 1988. The International Gustav Mahler Society was founded in 1955 in Vienna, with Bruno Walter as its first President and Alma Mahler as an honorary member. The Society aims to create a complete critical edition of Mahler's works, and to commemorate all aspects of the composer's life.

Among other composers whose work carries the influence of Mahler, Mitchell lists America's Aaron Copland, the German song and stage Composer Kurt Weill, Italy's Luciano Berio, Russia's Dmitri Shostakovich and England's Benjamin Britten. The American composers Leonard Bernstein and Samuel Barber were also influenced by Mahler's work. In a 1989 interview the pianist-conductor Vladimir Ashkenazy said that the connection between Mahler and Shostakovich was "very strong and obvious"; their music represented "the individual versus the vices of the world." Mitchell highlights Britten's "marvellously keen, spare and independent writing for the wind in ... the first movement of the Cello Symphony of 1963 [which] clearly belongs to that order of dazzling transparency and instrumental emancipation which Mahler did so much to establish." Mitchell concludes with the statement: "Even were his own music not to survive, Mahler would still enjoy a substantial immortality in the music of these pre-eminent successors who have embraced his art and assimilated his techniques."

Deryck Cooke argues that Mahler's popularity escalated when a new, postwar generation of music-lovers arose, untainted by "the dated polemics of anti-romanticism" which had affected Mahler's reputation in the inter-war years. In this more liberated age, enthusiasm for Mahler expanded even into places—Spain, France, Italy—which had long been resistant to him. Robert Carr's simpler explanation for the 1950s Mahler revival is that "it was the long-playing record [in the early 1950s] rather than the Zeitgeist which made a comprehensive breakthrough possible. Mahler's work became accessible and repeatable in the home." In the years following his centenary in 1960, Mahler rapidly became one of the most performed and most recorded of all composers, and has largely remained thus. In Britain and elsewhere, Carr notes, the extent of Mahler performances and recordings has replaced a relative famine with a glut, bringing problems of over-familiarity. Harold Schonberg comments that "it is hard to think of a Composer who arouses equal loyalty," adding that "a response of anything short of rapture to the Mahler symphonies will bring [to the critic] long letters of furious denunciation."