He was sent to Lovedale High School in 1964, a prestigious boarding school in Alice, Eastern Cape, where his older brother Kahya had previously been studying. During the Apartheid in South Africa, with no freedom of association protection for non-Afrikaner South African's, Biko was expelled from Lovedale for his political views, and his brother arrested for his alleged association with Poqo (now known as the Azanian People's Liberation Army). After being expelled, he then attended and later graduated from St. Francis College, a Roman Catholic institution in Mariannhill, Natal.
He studied to be a doctor at the University of Natal Medical School. Biko was a Xhosa. In addition to Xhosa, he spoke fluent English and fairly fluent Afrikaans.
Biko married Ntsiki Mashalaba in 1970. They had two children together: Nkosinathi, born in 1971, and Samora. He also had two children with Dr Mamphela Ramphele (a prominent activist within the BCM): a daughter, Lerato, born in 1974, who died of pneumonia when she was only two months old, and a son, Hlumelo, who was born in 1978, after Biko's death. Biko also had a daughter with Lorraine Tabane, named Motlatsi, born in May 1977.
In the early 1970s Biko became a key figure in The Durban Moment. In 1972 he was expelled from the University of Natal because of his political activities and he became honorary president of the Black People's Convention. He was banned by the apartheid regime in February 1973, meaning that he was not allowed to speak to more than one person at a time nor to speak in public, was restricted to the King William's Town magisterial district, and could not write publicly or speak with the media. It was also forbidden to quote anything he said, including speeches or simple conversations.
When Biko was banned, his movement within the country was restricted to the Eastern Cape, where he was born. After returning there, he formed a number of grassroots organizations based on the notion of self-reliance: Zanempilo, the Zimele Trust Fund (which helped support former political prisoners and their families), Njwaxa Leather-Works Project and the Ginsberg Education Fund.
In spite of the repression of the apartheid government, Biko and the BCM played a significant role in organising the protests which culminated in the Soweto Uprising of 16 June 1976. In the aftermath of the uprising, which was crushed by heavily armed police shooting school children protesting, the authorities began to target Biko further.
On 11 September 1977, police loaded him in the back of a Land Rover, naked and restrained in manacles, and began the 1100 km drive to Pretoria to take him to a prison with hospital facilities. He was nearly dead owing to the previous injuries. He died shortly after arrival at the Pretoria prison, on 12 September. The police claimed his death was the result of an extended hunger strike, but an autopsy revealed multiple bruises and abrasions and that he ultimately succumbed to a brain hemorrhage from the massive injuries to the head, which many saw as strong evidence that he had been brutally clubbed by his captors. Then Donald Woods, a journalist, editor and close friend of Biko's, along with Helen Zille, later leader of the Democratic Alliance political party, exposed the truth behind Biko's death.
Because of his high profile, news of Biko's death spread quickly, opening many eyes around the world to the brutality of the apartheid regime. His funeral was attended by over 10,000 people, including numerous ambassadors and other diplomats from the United States and Western Europe. The liberal white South African journalist Donald Woods, a personal friend of Biko, photographed his injuries in the morgue. Woods was later forced to flee South Africa for England. Donald Woods later campaigned against apartheid and further publicised Biko's life and death, writing many newspaper articles and authoring the book, Biko, which was later turned into the film Cry Freedom. Speaking at a National Party conference following the news of Biko's death then-minister of police, Jimmy Kruger said, "I am not glad and I am not sorry about Mr. Biko. It leaves me cold (Dit laat my koud). I can say nothing to you ... Any person who dies ... I shall also be sorry if I die."