Born in Halberstadt, Germany the son of a post-office employee, Bormann dropped out of school to work on a farm in Mecklenburg. After serving briefly at the end of WW I, Bormann joined the Freikorps in Mecklenburg.
In March 1924 he received a one year sentence as an accomplice to his friend Rudolf Höss (the later commandant of Auschwitz) in the brutal murder of Walther Kadow (who may have 'betrayed' Leo Schlageter to the French in the Ruhr).
After his release he joined the NSDAP in Thuringia, and despite his apparent lack of skill and a coarse and brutal manner, became its regional press officer, and later, business manager in 1928. In October 1933 he became a Reichsleiter of the NSDAP and in November a member of the Reichstag. From July 1933 until 1941 Bormann was personal secretary to Rudolf Hess.
The flight of Rudolf Hess to Britain allowed Bormann to become head of the Parteikanzlei in May 1941 and he proved himself a master of political in-fighting. He developed and administered the Adolf Hitler Endowment Fund of German industry, a huge fund of 'voluntary' contributions by successful business entrepreneurs to the Führer, which Bormann then reallocated as gifts to almost all the top Party functionaries. In addition to administering Hitler's personal finances Bormann took charge of all Hitler's paperwork and appointments. Hitler came to have complete trust in Bormann and the view of reality that he presented.
At the end of the war, after the suicide of Hitler, Bormann left the Führerbunker in Berlin on April 30 1945. It is widely believed he was killed by Soviet troops not long after leaving the bunker. He was tried and sentenced to death in absentia at Nuremberg in October 1946. His court-appointed defense attorney used the unusual and unsuccessful defense that Bormann could not be convicted because he was already dead. A skeleton found near the site of the old Reich Chancellory in Berlin in 1972 was officially identified as Bormann and he was formally pronounced dead by a West German court in April 1973. Subsequent examination has confirmed that this was indeed Bormann's corpse; however, there is evidence that he had survived after 1945—the skull showed evidence of dental work that is unrecorded in his medical records, and there were traces of South American soil, supporting theories that Bormann had escaped to South America after the war and died and had been buried there before his corpse was repatriated to Berlin.
He was married to Gerda Buch (daughter of the Supreme Party Judge, Walter Buch) and had ten children. Martin Bormann Jr. (born 1930) converted to catholicism and served as a priest in Africa.