Reinhard Tristan Eugen Heydrich was born in 1904 in Halle an der Saale to Composer and opera singer Richard Bruno Heydrich and his wife, Elisabeth Anna Maria Amalia Heydrich (née Krantz). His father was Protestant and his mother was Roman Catholic. His two forenames were patriotic musical tributes: "Reinhard" referred to the tragic hero from his father's opera Amen, and "Tristan" stems from Richard Wagner's Tristan und Isolde. Heydrich's third name, "Eugen", was his late maternal grandfather's forename (Professor Eugen Krantz had been the Director of the Dresden Royal Conservatory).

In 1918, World War I ended with Germany's defeat. In late February 1919, civil unrest—including strikes and clashes between communist and anti-communist groups—took place in Heydrich's home town of Halle. Under Defense Minister Gustav Noske's directives, a right-wing paramilitary unit was formed and ordered to "recapture" Halle. Heydrich, then 15 years old, joined Maercker's Volunteer Rifles (a paramilitary Freikorps unit). When the skirmishes ended, Heydrich was part of the force assigned to protect private property. Little is known about his role, but the events left a strong impression; it was a "political awakening" for him. He joined the Deutschvölkischer Schutz und Trutzbund (National German Protection and Shelter League), an anti-Semitic organisation.

As a result of the conditions of the Treaty of Versailles, hyperinflation spread across Germany and many lost their life savings. Halle was not spared. By 1921, few townspeople there could afford a musical education at Bruno Heydrich's conservatory. This led to a financial crisis for the Heydrich family.

In 1922, Heydrich joined the German Navy (Reichsmarine), taking advantage of the security, structure, and pension it offered. He became a naval cadet at Kiel, Germany's primary naval base. On 1 April 1924 he was promoted to senior midshipman (Oberfähnrich zur See) and sent to officer training at the Naval Academy Mürwik. In 1926 he advanced to the rank of ensign (Leutnant zur See) and was assigned as a signals officer on the battleship Schleswig-Holstein, the flagship of Germany's North Sea Fleet. With the promotion came greater recognition. He received good evaluations from his superiors and had few problems with other crewmen. He was promoted on 1 July 1928 to the rank of sub-lieutenant (Oberleutnant zur See). The increased rank fuelled his ambition and arrogance.

Heydrich was said to despise the Concentration Camp Service and held a particular derision for Theodor Eicke, whom he referred to as an "ambitious dwarf". Heydrich had little to do with and did not trust Oswald Pohl. He characterised Rudolf Höss, commander of Auschwitz, as an uneducated thug. Within upper SS administration, Heydrich was friendly towards Karl Wolff. In later years, Wolff said he was always wary of Heydrich, who seemed to be waiting for an opportunity to move against him and disgrace him with Himmler. Within the Allgemeine SS, Heydrich forged relationships with some of the more powerful SS and Police Leaders such as Friedrich Jeckeln. Heydrich maintained a dialogue with him, but cautiously, especially after Jeckeln ran afoul of Himmler in the late 1930s and early 1940s.

On 1 August 1931, Heydrich began his job as chief of the new 'Ic Service' (intelligence service). He set up office at the Brown House, the Nazi Party headquarters in Munich. By October he had created a network of spies and informers for intelligence-gathering purposes and to obtain information to be used as blackmail to further political aims. Information on thousands of people was recorded on index cards and stored at the Brown House. To mark the occasion of Heydrich's December wedding, Himmler promoted him to the rank of SS-Sturmbannführer (major).

In mid-1932, Himmler appointed Heydrich chief of the renamed security service—the Sicherheitsdienst (SD). Heydrich's counterintelligence Service grew into an effective machine of terror and intimidation. With Hitler striving for absolute power in Germany, Himmler and Heydrich wished to control the political police forces of all 17 German states. They began with Bavaria. In 1933, Heydrich gathered some of his men from the SD and together they stormed police headquarters in Munich and took over the organisation using intimidation tactics. Himmler became the Munich police chief and Heydrich became the commander of Department IV, the political police.

In 1933, Hitler became Chancellor of Germany, and through a series of decrees became Germany's Führer und Reichskanzler (leader and chancellor). The first concentration camps, which were originally intended to house political opponents, were established in early 1933. By year's end there were over fifty camps.

Beginning in April 1934, and at Hitler's request, Heydrich and Himmler began building a dossier on Sturmabteilung (SA) leader Ernst Röhm in an effort to remove him as a rival for party leadership. At this point, the SS was still part of the SA, the early Nazi paramilitary organisation which now numbered over 3 million men. At Hitler's direction, Heydrich, Himmler, Göring, and Viktor Lutze drew up lists of those who should be killed, starting with seven top SA officials and including many more. On 30 June 1934 the SS and Gestapo acted in coordinated mass arrests that continued for two days. Röhm was shot without trial, along with the leadership of the SA. The purge became known as the Night of the Long Knives. Up to 200 people were killed in the action. Lutze was appointed SA's new head and it was converted into a Sports and training organisation.

In 1936, Heydrich learned that a top-ranking Soviet officer was plotting to overthrow Joseph Stalin. Sensing an opportunity to strike a blow at both the Soviet Army and Admiral Canaris of Germany's Abwehr, Heydrich decided that the Russian officers should be "unmasked". He discussed the matter with Himmler and both in turn brought it to Hitler's attention. But the "information" Heydrich had received was actually misinformation planted by Stalin himself in an attempt to legitimise his planned purges of the Red Army's high command. Stalin ordered one of his best NKVD agents, General Nikolai Skoblin, to pass Heydrich false information suggesting that Marshal Mikhail Tukhachevsky and other Soviet generals were plotting against Stalin. Hitler approved Heydrich's plan to act on the information immediately. Heydrich's SD forged documents and letters implicated Tukhachevsky and other Red Army commanders. The material was delivered to the NKVD. The Great Purge of the Red Army followed on Stalin's orders. While Heydrich believed they had successfully deluded Stalin into executing or dismissing 35,000 of his officer corps, the importance of Heydrich's part is a matter of speculation and conjecture. Soviet military prosecutors did not use the forged documents against the generals in their secret trial; they instead relied on false confessions extorted or beaten out of the defendants.

In January 1937, Heydrich directed the SD to secretly begin collecting and analysing public opinion and report back its findings. He then had the Gestapo carry out house searches, arrests, and interrogations, thus in effect exercising control over public opinion. In February 1938 when the Austrian Chancellor Kurt Schuschnigg resisted Hitler's proposed merger with Germany, Heydrich intensified the pressure on Austria by organising Nazi demonstrations and distributing propaganda in Vienna stressing the Common Germanic blood of the two countries. In the Anschluss on 12 March, Hitler declared the unification of Austria with Nazi Germany.

Heydrich was one of the organisers of Kristallnacht, a pogrom against Jews throughout Germany on the night of 9–10 November 1938. Heydrich sent a telegram that night to various SD and Gestapo offices, helping to co-ordinate the pogrom with the SS, SD, Gestapo, uniformed police (Orpo), SA, Nazi party officials, and even the fire departments. It talks about permitting arson and destroying Jewish businesses and synagogues, and orders the confiscation of all "archival material" out of Jewish community centres and synagogues. The telegram ordered that "as many Jews – particularly affluent Jews – are to be arrested in all districts as can be accommodated in existing detention facilities ... Immediately after the arrests have been carried out, the appropriate concentration camps should be contacted to place the Jews into camps as quickly as possible." Twenty thousand Jews were sent to concentration camps in the days immediately following; historians consider Kristallnacht the beginning of the Holocaust.

On 29 November 1939, Heydrich issued a cable about the "Evacuation of New Eastern Provinces", detailing the deportation of people by railway to concentration camps, and giving guidance surrounding the December 1939 census, which would be the basis on which those deportations were performed. In May 1941 Heydrich drew up regulations with Quartermaster general Eduard Wagner for the upcoming invasion of the Soviet Union, which ensured that the Einsatzgruppen and army would co-operate in murdering Soviet Jews.

By late 1940, German armies had swept through most of Western Europe. The following year, Heydrich's SD was given responsibility for carrying out the Nacht und Nebel (Night-and-Fog) decree. According to the decree, "persons endangering German security" were to be arrested in a maximally discreet way: "under the cover of night and fog". People disappeared without a trace with none told of their whereabouts or fate. For each prisoner, the SD had to fill in a questionnaire that listed personal information, country of origin, and the details of their crimes against the Reich. This questionnaire was placed in an envelope inscribed with a seal reading "Nacht und Nebel" and submitted to the Reich Main Security Office (RSHA). In the WVHA "Central Inmate File", as in many camp files, these prisoners would be given a special "covert prisoner" code, as opposed to the code for POW, Felon, Jew, Gypsy, etc. The decree remained in effect after Heydrich's death. The exact number of people who vanished under it has never been positively established, but it is estimated to be 7,000.

Heydrich's time in the SS was a mixture of rapid promotions, reserve commissions in the regular armed forces, and front-line combat Service. During his 11 years with the SS Heydrich "rose from the ranks" and was appointed to every rank from private to full general. He was also a major in the Luftwaffe, flying nearly 100 combat missions until 22 July 1941, when his plane was hit by Soviet anti-aircraft fire. Heydrich made an emergency landing behind enemy lines. He evaded a Soviet patrol and contacted a forward German patrol. After this Hitler personally ordered Heydrich to return to Berlin to resume his SS duties. His Service record also gives him credit as a Navy Reserve Lieutenant, although during World War II Heydrich had no contact with this military branch.

Heydrich's replacements were Ernst Kaltenbrunner as the chief of RSHA, and Karl Hermann Frank (27–28 May 1942) and Kurt Daluege (28 May 1942 – 14 October 1943) as the new acting Reichsprotektors. After Heydrich's death, implementation of the policies formalised at the Wannsee conference he chaired was accelerated. The first three true death camps, designed for mass killing with no legal process or pretext, were built and operated at Treblinka, Sobibór, and Bełżec. The project was named Operation Reinhard after Heydrich.

Heydrich's widow Lina won the right to a pension following a series of court cases against the West German government in 1956 and 1959. She was declared entitled to a substantial pension as her husband was a German general killed in action. The government had previously declined to pay due to Heydrich's role in the Holocaust. The couple had four children: Klaus, born in 1933, killed in a traffic accident in 1943; Heider, born in 1934; Silke, born in 1939; and Marte, born shortly after her father's death in 1942. Lina wrote a memoir, Leben mit einem Kriegsverbrecher (Living With a War Criminal), which was published in 1976. She remarried once and died in 1985.

All but four of the women from Lidice were deported immediately to Ravensbrück concentration camp (four were pregnant – they were subjected to forced abortions at the same hospital where Heydrich had died and the women were then sent to the concentration camp). Some children were chosen for Germanization, and 81 were killed in gas vans at the Chełmno extermination camp. Both towns were burned and Lidice's ruins were levelled. At least 1,300 people were massacred after Heydrich's death.

Heydrich was interred in Berlin's Invalidenfriedhof, a military cemetery. The exact burial spot is not known—a temporary wooden marker that disappeared when the Red Army overran the city in 1945 was never replaced, so that Heydrich's grave could not become a rallying point for Neo-Nazis. A photograph of Heydrich's burial shows the wreaths and mourners to be in section A, which abuts the north wall of the Invalidenfriedhof and Scharnhorststraße, at the front of the cemetery. A recent biography of Heydrich also places the grave in Section A. Hitler planned for Heydrich to have a monumental tomb (designed by Sculptor Arno Breker and Architect Wilhelm Kreis) but, due to Germany's declining fortunes, it was never built.