Lomax was born in Austin, Texas, in 1915, the third of four children born to Bess Brown and pioneering folklorist and author John A. Lomax.

Due to childhood asthma, chronic ear infections, and generally frail health, Lomax had mostly been home schooled in elementary school. In Dallas, he entered the Terrill School for Boys (a tiny prep school that later became St. Mark's School of Texas). Lomax excelled at Terrill and then transferred to the Choate School (now Choate Rosemary Hall) in Connecticut for a year, graduating eighth in his class at age 15 in 1930.

Lomax, now 17, therefore took a break from studying to join his father's folk song collecting field trips for the Library of Congress, co-authoring American Ballads and Folk Songs (1934) and Negro Folk Songs as Sung by Lead Belly (1936). His first field collecting without his Father was done with Zora Neale Hurston and Mary Elizabeth Barnicle in the summer of 1935. He returned to the University of Texas that fall and was awarded a BA in Philosophy, summa cum laude, and membership in Phi Beta Kappa in May 1936. Lack of money prevented him from immediately attending graduate school at the University of Chicago, as he desired, but he would later correspond with and pursue graduate studies with Melville J. Herskovits at Columbia University and with Ray Birdwhistell at the University of Pennsylvania.

From 1937-42, Lomax was Assistant in Charge of the Archive of Folk Song of the Library of Congress to which he and his Father and numerous collaborators contributed more than ten thousand field recordings. A pioneering oral Historian, Lomax recorded substantial interviews with many folk and jazz Musicians, including Woody Guthrie, Lead Belly, Muddy Waters, Jelly Roll Morton and other jazz pioneers, and Big Bill Broonzy. He also initiated some of the first (if not the very first) "man-on-the street" radio interviews of ordinary citizens.

As part of this work, Lomax traveled through Michigan and Wisconsin in 1938 to record and document the traditional music of that region. Over four hundred recordings from this collection are now available at the Library of Congress. "He traveled in a 1935 Plymouth sedan, toting a Presto instantaneous disc recorder and a movie camera. And when he returned nearly three months later, having driven thousands of miles on barely paved roads, it was with a cache of 250 discs and 8 reels of film, documents of the incredible range of ethnic diversity, expressive traditions, and occupational folklife in Michigan."

In late 1939, Lomax hosted two series on CBS's nationally broadcast American School of the Air, called American Folk Song and Wellsprings of Music, both music appreciation courses that aired daily in the schools and were supposed to highlight links between American folk and classical orchestral music. As host, Lomax sang and presented other performers, including Burl Ives, Woody Guthrie, Lead Belly, Pete Seeger, Josh White, and the Golden Gate Quartet. The individual programs reached ten million students in 200,000 U.S. classrooms and were also broadcast in Canada, Hawaii, and Alaska, but both Lomax and his Father felt that the concept of the shows, which portrayed folk music as mere raw material for orchestral music, was deeply flawed and failed to do justice to vernacular culture.

As a member of the Popular Front and People's Songs in the 1940s, Alan Lomax promoted what was then known as "One World" and today is called multiculturalism. In the late forties he produced a series of concerts at Town Hall and Carnegie Hall that presented flamenco guitar and calypso, along with country blues, Appalachian music, Andean music, and jazz. His radio shows of the 1940s and 1950s explored musics of all the world's peoples.

On December 8, 1941, as "Assistant in Charge at the Library of Congress", he sent telegrams to fieldworkers in ten different localities across the United States, asking them to collect reactions of ordinary Americans to the bombing of Pearl Harbor and the subsequent declaration of war by the United States. A second series of interviews, called "Dear Mr. President", was recorded in January and February 1942.

In June 1942 the FBI approached the Librarian of Congress, Archibald McLeish, in an attempt to have Lomax fired as Assistant in Charge of the Library's Archive of American Folk Song. At the time, Lomax was preparing for a field trip to the Mississippi Delta on behalf of the Library, where he would make landmark recordings of Muddy Waters, Son House, and David "Honeyboy" Edwards, among others. McLeish wrote to Hoover, defending Lomax: "I have studied the findings of these reports very carefully. I do not find positive evidence that Mr. Lomax has been engaged in subversive activities and I am therefore taking no disciplinary action toward him." Nevertheless, according to Gioia:

While serving in the Army in World War II Lomax produced and hosted numerous radio programs in connection with the war effort. The 1944 "ballad opera", The Martins and the Coys, broadcast in Britain (but not the USA) by the BBC, featuring Burl Ives, Woody Guthrie, Will Geer, Sonny Terry, Pete Seeger, and Fiddlin' Arthur Smith, among others, was released on Rounder Records in 2000.

Lomax, who was a founding member of People's Songs, was in charge of campaign music for Henry A. Wallace's 1948 Presidential run on the Progressive Party ticket on a platform opposing the arms race and supporting civil rights for Jews and African Americans. Subsequently, Lomax was one of the performers listed in the publication Red Channels as a possible Communist sympathizer and was consequently blacklisted from working in US entertainment industries.

Lomax recognized that folklore (like all forms of creativity) occurs at the local and not the national level and flourishes not in isolation but in fruitful interplay with other cultures. He was dismayed that mass communications appeared to be crushing local cultural expressions and languages. In 1950 he echoed Anthropologist Bronisław Malinowski (1884–1942), who believed the role of the ethnologist should be that of advocate for primitive man (as indigenous people were then called), when he urged Folklorists to similarly advocate for the folk. Some, such as Richard Dorson, objected that scholars shouldn't act as cultural arbiters, but Lomax believed it would be unethical to stand idly by as the magnificent variety of the world's cultures and languages was "grayed out" by centralized commercial entertainment and educational systems. Although he acknowledged potential problems with intervention, he urged that Folklorists with their special training actively assist communities in safeguarding and revitalizing their own local traditions.

Lomax and Diego Carpitella's survey of Italian folk music for the Columbia World Library, conducted in 1953 and 1954, with the cooperation of the BBC and the Accademia Nazionale di Santa Cecilia in Rome, helped capture a snapshot of a multitude of important traditional folk styles shortly before they disappeared. The pair amassed one of the most representative folk song collections of any culture. From Lomax's Spanish and Italian recordings emerged one of the first theories explaining the types of folk singing that predominate in particular areas, a theory that incorporates work style, the environment, and the degrees of social and sexual freedom.

The FBI again investigated Lomax in 1956 and sent a 68-page report to the CIA and the Attorney General's office. However, william Tompkins, assistant attorney general, wrote to Hoover that the investigation had failed to disclose sufficient evidence to warrant prosecution or the suspension of Lomax's passport.

Upon his return to New York in 1959, Lomax produced a concert, Folksong '59, in Carnegie Hall, featuring Arkansas singer Jimmy Driftwood; the Selah Jubilee Singers and Drexel Singers (gospel groups); Muddy Waters and Memphis Slim (blues); Earl Taylor and the Stoney Mountain Boys (bluegrass); Pete Seeger, Mike Seeger (urban folk revival); and The Cadillacs (a rock and roll group). The occasion marked the first time rock and roll and bluegrass were performed on the Carnegie Hall Stage. "The time has come for Americans not to be ashamed of what we go for, musically, from primitive ballads to rock 'n' roll songs", Lomax told the audience. According to Izzy Young, the audience booed when he told them to lay down their prejudices and Listen to rock 'n' roll. In Young's opinion, "Lomax put on what is probably the turning point in American folk music . . . . At that concert, the point he was trying to make was that Negro and white music were mixing, and rock and roll was that thing."

When Columbia Records Producer George Avakian gave jazz arranger Gil Evans a copy of the Spanish World Library LP, Miles Davis and Evans were "struck by the beauty of pieces such as the 'Saeta', recorded in Seville, and a panpiper's tune ('Alborada de Vigo') from Galicia, and worked them into the 1960 album, Sketches of Spain."

Lomax married Antoinette Marchand on August 26, 1961. They separated the following year and were divorced in 1967.

In 1962, Lomax and singer and Civil Rights Activist Guy Carawan, music Director at the Highlander Folk School in Monteagle, Tennessee, produced the album, Freedom in the Air: Albany Georgia, 1961-62, on Vanguard Records for the Student Nonviolent Coordinating Committee.

The FBI investigation was concluded the following year, shortly after Lomax's 65th birthday.

Similar ideas had been put into practice by Benjamin Botkin, Harold W. Thompson, and Louis C. Jones, who believed that folklore studied by Folklorists should be returned to its home communities to enable it to thrive anew. They have been realized in the annual (since 1967) Smithsonian Folk Festival on the Mall in Washington, D.C. (for which Lomax served as a consultant), in national and regional initiatives by public Folklorists and local Activists in helping communities gain recognition for their oral traditions and lifeways both in their home communities and in the world at large; and in the National Heritage Awards, concerts, and fellowships given by the NEA and various State governments to master folk and traditional artists.

Then, as late as 1979, an FBI report suggested that Lomax had recently impersonated an FBI agent. The report appears to have been based on mistaken identity. The person who reported the incident to the FBI said that the man in question was around 43, about 5 feet 9 inches and 190 pounds. The FBI file notes that Lomax stood 6 feet (1.8 m) tall, weighed 240 pounds and was 64 at the time:

In 1983, Lomax founded The Association for Cultural Equity (ACE). It is housed at the Fine Arts Campus of Hunter College in New York City and is the custodian of the Alan Lomax Archive. The Association's mission is to "facilitate cultural equity" and practice "cultural feedback" and "preserve, publish, repatriate and freely disseminate" its collections. Though Alan Lomax's appeals to anthropology conferences and repeated letters to UNESCO fell on deaf ears, the modern world seems to have caught up to his vision. In an article first published in the 2009 Louisiana Folklore Miscellany, Barry Jean Ancelet, folklorist and chair of the Modern Languages Department at University of Louisiana at Lafayette, wrote:

On August 24, 1997, at a concert at Wolf Trap, Vienna, Virginia, Bob Dylan had this to say about Lomax, who had helped introduce him to folk music and whom he had known as a young man in Greenwich Village:

In 2001, in the wake of the attacks in New York and Washington of September 11, UNESCO's Universal Declaration of Cultural Diversity declared the safeguarding of languages and intangible culture on a par with protection of individual human rights and as essential for human survival as biodiversity is for nature, ideas remarkably similar to those forcefully articulated by Alan Lomax many years before.

Lomax was a consultant to Carl Sagan for the Voyager Golden Record sent into space on the 1977 Voyager Spacecraft to represent the music of the earth. Music he helped choose included the blues, jazz, and rock 'n' roll of Blind Willie Johnson, Louis Armstrong, and Chuck Berry; Andean panpipes and Navajo chants; Azerbaijani mugham performed by two balaban players, a Sicilian sulfur miner's lament; polyphonic vocal music from the Mbuti Pygmies of Zaire, and the Georgians of the Caucasus; and a shepherdess song from Bulgaria by Valya Balkanska; in addition to Bach, Mozart, and Beethoven, and more. Sagan later wrote that it was Lomax "who was a persistent and vigorous advocate for including ethnic music even at the expense of Western classical music. He brought pieces so compelling and beautiful that we gave in to his suggestions more often than I would have thought possible. There was, for Example, no room for Debussy among our selections, because Azerbaijanis play bagpipe-sounding instruments [balaban] and Peruvians play panpipes and such exquisite pieces had been recorded by Ethnomusicologists known to Lomax." He died in Safety Harbor, Florida on July 19, 2002 at the age of 87.

Alan Lomax received the National Medal of Arts from President Ronald Reagan in 1986; a Library of Congress Living Legend Award in 2000; and was awarded an Honorary Doctorate in Philosophy from Tulane University in 2001. He won the National Book Critics Circle Award and the Ralph J. Gleason Music Book Award in 1993 for his book The Land Where the Blues Began, connecting the story of the origins of blues music with the prevalence of forced labor in the pre-World War II South (especially on the Mississippi levees). Lomax also received a posthumous Grammy Trustees Award for his lifetime achievements in 2003. Jelly Roll Morton: The Complete Library of Congress Recordings by Alan Lomax (Rounder Records, 8 CDs boxed set) won in two categories at the 48th annual Grammy Awards ceremony held on Feb 8, 2006 Alan Lomax In Haiti: Recordings For The Library Of Congress, 1936–1937, issued by Harte Records and made with the support and major funding from Kimberley Green and the Green foundation, and featuring 10 CDs of recorded music and film footage (shot by Elizabeth Lomax, then nineteen), a bound book of Lomax's selected letters and field journals, and notes by musicologist Gage Averill, was nominated for two Grammy Awards in 2011.

A 2007 BBC news article revealed that in the early 1950s, the British MI5 placed Alan Lomax under surveillance as a suspected Communist. Its report concluded that although Lomax undoubtedly held "left wing" views, there was no evidence he was a Communist. Released September 4, 2007 (File ref KV 2/2701), a summary of his MI5 file reads as follows:

In January 2012, the American Folklife Center at the Library of Congress, with the Association for Cultural Equity, announced that they would release Lomax's vast archive in digital form. Lomax spent the last 20 years of his life working on an interactive multimedia educational computer project he called the Global Jukebox, which included 5,000 hours of sound recordings, 400,000 feet of film, 3,000 videotapes, and 5,000 photographs. By February 2012, 17,000 music tracks from his archived collection were expected to be made available for free streaming, and later some of that music may be for sale as CDs or digital downloads. As of March 2012 this has been accomplished. Approximately 17,400 of Lomax's recordings from 1946 and later have been made available free online. This is material from Alan Lomax’s independent archive, begun in 1946, which has been digitized and offered by the Association for Cultural Equity. This is "distinct from the thousands of earlier recordings on acetate and aluminum discs he made from 1933 to 1942 under the auspices of the Library of Congress. This earlier collection — which includes the famous Jelly Roll Morton, Woody Guthrie, Lead Belly, and Muddy Waters sessions, as well as Lomax’s prodigious collections made in Haiti and Eastern Kentucky (1937) — is the provenance of the American Folklife Center" at the library of Congress.