She was born Doris Amelia Hordern in Melbourne, Victoria, and became involved in women's rights and peace issues from a young age and served as the campaign secretary of Vida Goldstein, the first woman to stand for election to federal parliament in Australia. She married Maurice Blackburn, a fellow firebrand socialist, in 1914 and spent their honeymoon organising anti-war and anti-conscription campaigns.
While her husband served at different times as a Labor member of the Victorian and Federal parliaments, Blackburn continued to work on social issues, some of which brought her into conflict with the Labor Party (of which she too was a member) and following Maurice’s expulsion from the party in 1937, Doris resigned from the ALP. Maurice continued to sit in parliament as an independent but lost his seat at the 1943 federal election to the official Labor candidate, and died the following year.
Upset at Labor’s treatment of her husband, Doris stood as an Independent Labour candidate for Maurice’s old seat of Bourke at the 1946 election, winning it and in doing so became only the second woman to be elected to the Australian House of Representatives. In parliament Blackburn, who shared the cross benches with fellow former Labor member Jack Lang, championed similar issues to her late husband, gaining nationwide notoriety in 1947 as the only MP to vote against the Atomic Energy Bill, and served as the national President of the Council for Civil Liberties. Following an electoral redistribution, her seat of Bourke was abolished, leaving Blackburn to run for the newly established seat of Wills, which she lost to the Labor Party.
Blackburn continued to be active in social issues, serving as president of the Women's International League for Peace and Freedom and co-founding, with Douglas Nicholls, the Aborigines Advancement League and the Federal Council for Advancement of Aborigines and Torres Strait Islanders.
Blackburn died in Coburg, Victoria.