Abraham Louis Fischer (23 April 1908 – 8 May 1975) was a South African Communist lawyer of Afrikaner descent with partial Anglo-African ancestry from his paternal grandmother, notable for anti-apartheid activism and for the legal defence of anti-apartheid figures, including Nelson Mandela, at the Rivonia Trial. Following the trial, he was himself put on trial accused of furthering communism. He was sentenced to life imprisonment and diagnosed with cancer while in prison. The South African Prisons Act was extended to include his brother's house in Bloemfontein, where he died two months later.

Fischer came from a prominent Afrikaner family; his father was Percy Fischer (1878–1957), a judge president of the Orange Free State and his grandfather was Abraham Fischer (1850–1913), a prime minister of the Orange River Colony and later a member of the cabinet of the unified South Africa.

Prior to studying at University of Oxford (New College) as a Rhodes scholar during the 1930s, he was schooled at Grey College and Grey University College in Bloemfontein, he was a resident of House Abraham Fischer which is named after his grandfather Abraham Fischer. During his stay at Oxford, he travelled on the European continent, including a trip in 1932 to the Soviet Union. In a letter to his parents during his trip indicating that he had become radicalized, he noted similarities between the position of Russian farmers that he encountered along the Volga river and South African blacks.

In 1937, Fischer married Molly Krige, a niece of Jan Smuts; the couple had three children. Their son, Paul died of cystic fibrosis at the age of 23 while Fischer was in prison. Molly became involved in politics and was detained without trial during the 1960 state of emergency declared after the Sharpeville massacre. In 1964, Bram, Molly and a friend, Liz Franklin, were driving to Cape Town for daughter Ilse's 21st birthday. Bram swerved the car to avoid hitting a cow that had strayed onto the road. The car veered off the road and overturned into a river, causing Molly to drown.

Fischer joined the Communist Party of South Africa (SACP) in the 1940s and soon rose to leadership positions. The CPSA had a close relationship with the African National Congress (ANC) and in 1943, Fischer co-authored revisions to the constitution of the ANC. In 1946 he was charged with incitement arising out of his position as a leader of the CPSA and the African Mine Workers' Strike of that year. After the CPSA was dissolved and banned in 1950, he became Chairman of the illegal South African Communist Party when it was established underground in 1953.

Alongside Issy Maisels and others, Fischer played an integral role on the defense team in the Treason Trial of 1956 – 1961 where Mandela and many other anti-apartheid activists were acquitted on 29 March 1961. In his autobiography, Mandela affectionately recalls Fischer reading the left wing publication New Age at his table during the trial proceedings.

Fischer led Nelson Mandela's legal defence team at the Rivonia Trial of 1963 – 1964. By a coincidence, Fischer had not been present at the raid on Liliesleaf Farm, although he had in fact been part of the trusted Rivonia inner circle. A number of documents seized by authorities were in his handwriting.

Mandela and co-defendants were sentenced to life imprisonment instead of the death penalty, which the state prosecutor Percy Yutar had been asking for. This was considered a victory for the defence. International pressure also played a role. At this time, Fischer's role as leader of the SACP was unknown even to his closest white friends.