Maurice McCrae Blackburn was born in Inglewood, Victoria, and educated at Melbourne Church of England Grammar School. After his father's death in 1887, the family was unable to pay for a university education. Blackburn began work as an office-boy.
Supporting himself by working as a teacher and librarian, Blackburn studied law and arts at the University of Melbourne (BA 1906; LLB 1909). He became a barrister, and in 1921 founded the legal firm of Maurice Blackburn & Co. Unusually for a firm of solicitors at the time, it specialised in trade union law.
Blackburn was increasingly involved in left-wing politics, in the Australian Labor Party and the Victorian Socialist Party. During World War I, he was one of the leaders of the campaign against conscription of Australians to fight in Europe. He also opposed wartime restrictions on civil liberties. As a result of his stand, he was defeated in the state election of 1917.
Re-elected to the Legislative Assembly, he introduced the Women's Qualifications Act (1926), which removed discrimination against women in a range of Acts of Parliament. His drafting skills and active role in the ALP were reflected in the party's objective of the socialisation of industry. Its qualified wording was devised by Blackburn in 1921 and long identified with him.
In the Australian Parliament from 1934, Blackburn maintained his concern with international pacifist issues, such as the rise of fascism. His relationship with the more isolationist, anti-communist groups in the ALP was sometimes hostile, and he was briefly expelled from the party in 1935.
In World War II, he again warned against harsh legislative restrictions and sweeping executive powers, now as president of the Australian Council for Civil Liberties. In 1941, Blackburn was expelled again from the ALP, over his support for the Soviet Union. He remained a vocal opponent of conscription for overseas service. When the House of Representatives voted for limited overseas conscription in 1943, he was in a minority of one.
Many who knew Blackburn felt strong affection for him. Friends and supporters provided financial help when he lost his seat in parliament in 1943. He died the following year, suffering from a cerebral tumor. A fellow member of the Victorian Parliament, Sir Frederic Eggleston, said Blackburn and his wife Doris were typical of 'the artless, intelligent, enthusiastic radical...unsuited to the hard conditions of Australian politics, yet willing to risk everything in their pursuit of their ideals'.