George Bizos, an anti-apartheid campaigner who served for nearly a half-century as Nelson Mandela’s personal lawyer, died Sept. 9 at 92.

The family announced the death but did not provide further details.

Mr. Bizos, who came to South Africa as a 13-year-old fleeing the Nazi occupation of Greece, played a key role in the legal fight to end apartheid, the racist system used to oppress South Africa’s Black majority for decades.

He represented Mandela from his treason trial in 1964 until the former South African president’s death in 2013. Mr. Bizos is credited with getting Mandela to add the words “if needs be” to his speech from the dock in which he said he was prepared to die for his ideals. The addition was seen as an escape clause, avoiding any impression that Mandela was goading the court to impose the death penalty.

During Mandela’s years in prison, Mr. Bizos helped to look after his family, and he played a key role in negotiations for Mandela’s release in 1990.

Mr. Bizos represented a wide range of people who defied apartheid, including the families of slain activists such as Steve Biko, and helped write the laws for the newly democratic country after apartheid ended with Mandela’s presidency in 1994.

After apartheid, Mr. Bizos was appointed to a committee that chose judges and worked to ensure the South African bench was racially representative. He also helped argue successfully for the abolition of the death penalty.

He remained active in human rights work in South Africa well into his 80s with the Legal Resources Center. In 2014, he questioned witnesses during an inquiry into the shooting deaths of several dozen protesters by police during a strike at Lonmin’s Marikana platinum mine in 2012.

Mr. Bizos considered himself Greek and South African to the core. During the struggle against apartheid, he said, he drew on his schooling in Greece about democracy and freedom.

He was born in November 1927 — the exact date was unclear — and his father was mayor of Vasilitsi. In 1941, he helped his father smuggle seven New Zealand soldiers out of Nazi-occupied Greece, and their rowboat was spotted days later by an Allied warship. They were taken to Egypt and spent time in a refugee camp before making their way to South Africa. (His mother remained in Greece for years.)

Upon arriving in Durban, he recalled, he was shocked by the inhumane treatment of “rickshaw boys . . . being treated like animals doing the work of beasts of burden.” He also faced prejudice as an immigrant in a country where apartheid rule was soon codified.

At the University of the Witwatersrand in Johannesburg, he was involved in leftist student politics. As a young lawyer in 1956, he helped defend Mandela and 155 other South Africans of all races who supported the Freedom Charter calling for a non-racial democracy and a socialist-based economy. All were acquitted.

Mr. Bizos later was part of the team credited with saving Mandela and others from the death penalty in the Rivonia Trial at which Mandela and seven others were convicted of sabotage and sentenced to life in prison.

Mr. Bizos’s efforts defending ordinary South Africans who ran up against apartheid laws brought home the tragedy of the racist system. In his 2007 memoir, “Odyssey to Freedom,” he wrote of teachers and parents trying to supplement the inferior education the White government designed for Black children. Their weekend and afternoon classes, called “cultural clubs,” were declared illegal.

Despite setbacks in court, Mr. Bizos was renowned for standing up to police and other officials who used brutal means to enforce apartheid.

“No South African lawyer did more to challenge the abuse of power by the security forces under apartheid,” Arthur Chaskalson, himself a respected anti-apartheid lawyer, wrote in 1998.

Mandela, who called Mr. Bizos “a man who combined a sympathetic nature with an incisive mind,” trusted him not only to represent him in court but later to carry messages from African National Congress leaders imprisoned on Robben Island to their colleagues in exile.

After Mandela’s release, Mr. Bizos lent his legal expertise to negotiations that led to South Africa’s first all-race elections in 1994. Mandela became the country’s first Black president.

In neighboring Zimbabwe in 2004, he defended opposition activist Morgan Tsvangirai in a treason case stemming from an alleged plot to assassinate that country’s longtime, increasingly autocratic president, Robert Mugabe. Tsvangirai was acquitted of treason, which carries the death penalty.

Mr. Bizos wrote in his memoir of learning, by studying American history, about the importance of protecting freedoms once they are gained.

“The lofty principles enunciated in a constitution or a bill of rights are no guarantee that these principles will be enforced or respected,” he said. “Much work and courage is needed to ensure they are maintained despite an ever-changing history.”

His wife, the former Arethe Daflos, died in 2017. Survivors include three sons and seven grandchildren.