Kani was born in New Brighton, Eastern Cape, South Africa.  His son Atandwa is also an actor and made his debut on U.S. television on the CW series Life Is Wild and played a younger version of his character T'Chaka in Black Panther.
After appearing in Athol Fugard's anti-apartheid play, "Sizwe Banzi Is Dead," which he also cowrote, Kani returned to South Africa. There he received a phone call saying that his father wanted to see him. On the way there, Kani says he was surrounded by police, who beat him and left him for dead. His left eye was lost in the incident and he now wears a prosthetic.
Kani joined the Serpent Players (a group of actors whose first performance was in the former snake pit of the zoo, hence the name) in Port Elizabeth in 1965 and helped to create many plays that went unpublished but were performed to a resounding reception.
These were followed by the more famous Sizwe Banzi is Dead and The Island, co-written with Athol Fugard and Winston Ntshona, in the early 1970s. He also received an Olivier Award nomination for his role in My Children! My Africa!
Kani's work has been widely performed around the world, including New York, where he and Winston Ntshona won a Tony Award in 1975 for Sizwe Banzi Is Dead and The Island. These two plays were presented in repertory at the Edison Theatre for a total of 52 performances.
In 1987 Kani played Othello in a performance of Shakespeare's play in South Africa which was still under apartheid. "At least I'll be able to kiss Desdemona without leaving a smudge." he said then.
Nothing but the Truth (2002) was his debut as sole playwright and was first performed in the Market Theatre in Johannesburg. This play takes place in post-apartheid South Africa and does not concern the conflicts between whites and blacks, but the rift between blacks who stayed in South Africa to fight apartheid, and those who left only to return when the hated regime folded. It won the 2003 Fleur du Cap Awards for best actor and best new South African play. In the same year he was also awarded a special Obie award for his extraordinary contribution to theatre in the United States.
Kani is executive trustee of the John Kani Theatre Foundation, founder and director of the John Kani Theatre Laboratory and chairman of the National Arts Council of SA. He starred as T'Chaka in the Marvel studios blockbusters Captain America: Civil War and Black Panther.
On 20 February 2010, Kani received Life Time award (SAFTA Awards). Kani has also received the Avanti Hall of Fame Award from the South African film, television and advertising industries, an M-Net Plum award and a Clio award in New York. Other awards include the Hiroshima Peace Culture Foundation Award for the year 2000 and the Olive Schreiner Prize for 2005. He was voted 51st in the Top 100 Great South Africans in 2004. In 2006, he was awarded an honorary doctorate by the University of Cape Town. Nelson Mandela Metropolitan University awarded him an honorary Doctor of Philosophy in 2013.
In 2016 Kani received the national honour of the Order of Ikhamanga in Silver, for his "Excellent contributions to theatre and, through this, the struggle for a non-racial, non-sexist and democratic South Africa".
Kani lost his eye when he returned to South Africa after appearing in Athol Fugard's anti-apartheid play, "Sizwe Banzi Is Dead," here and in New York. The actor was lured from his home by a telephone caller who said Kani was wanted at his father's home. On the way there, Kani says he was surrounded by police, who beat him and left him for dead.External link in