Sydney Kentridge was born in Johannesburg in 1922 and matriculated in 1938 at the King Edward VII High School. He married Felicia Geffen in 1952. They have two daughters, two sons, two granddaughters and two grandsons.
In 1941 he obtained the BA-degree at the University of the Witwatersrand. After his war service (1942 - 1946) he attended Exeter College, Oxford on an ex-serviceman's grant, where he took first class honours in jurisprudence. He was also made an Honorary Fellow of this College. Kentridge was furthermore awarded an honorary LL.D by the Universities of Cape Town, Natal, Leicester (England) and Seton Mall (New Jersey, USA). In 1973 he was a visiting scholar at Harvard Law School.
In 1949 Kentridge was admitted to the Johannesburg Bar and in 1965 he was appointed Senior Counsel. He served as Chairman of the Johannesburg Bar Council in 1972. In his early days at the Bar he appeared in several cases of historical and political significance, including cases for the Garment Workers' Union and its Secretary, E S "Solly" Sachs. He furthermore appeared as counsel at the inquiry into the shooting at Sharpeville, 1961, and for the family of Steve Biko at the inquest into his death. He also appeared for Stella Madzimabuto in both the then Rhodesia and the Privy Council in her challenge to the legality of the Smith regime.
Five years later he was called to the English Bar, and in 1984 he was appointed Queen's Counsel. He was an elected Bencher of Lincoln's Inn in 1986. In England Kentridge represented the English Bar in Court and acted for the British Government (in the litigation on the Maastricht Treaty) and against it (in litigation citing the Home Secretary for contempt of Court). He also appeared for William Shakespeare (in an action disputing his authorship, Middle Temple Hall 1968) and for the government of His Majesty George III (in trial for treason of George Washington, Lincoln's Inn, 1990).
From 1981 - 1986 he served as Judge of Appeal in Botswana and from 1988 - 1992 he was Judge of Appeal of Jersey and Guernsey.
Kentridge delivered the Roberts Lecture, University of Pennsylvania in 1979 and the first John Foster Memorial Lecture, London University, 1986 (both on civil rights in South Africa).