Nkoli was born in Soweto in a seSotho-speaking family. He grew up on a farm in the Free State and his family later moved to Sebokeng black township.
His activism started early. At age nine, he locked his parents in a wardrobe so they could escape detection from police enforcing the pass laws, which restricted where blacks could live.
The would-be activist found his boyfriend in 1974, Andre, a white bus driver, when he was just seventeen. Longing for companionship, he wrote to a white man he found in a gay magazine. The two men apparently hit it off and started a clandestine relationship.
When the couple’s parents found out, they forbade the men from seeing one another. Determined to be together, Nkoli and his white lover formed a suicide pact, which Nkoli’s parents also discovered.
Fearing for their son’s life, they begrudgingly allowed him to move to Johannesburg to be with his lover. Even while living together, however, the men had to remain undercover. Rather than going to jail for violating pass laws, Nkoli pretended to be a servant.
Nkoli became a youth activist against apartheid, with the Congress of South African Students (COSAS) and with the United Democratic Front, participating in the 1976 Soweto uprising.
In 1983, he joined the mainly white Gay Association of South Africa, then he formed the Saturday Group, the first black gay group in Africa.
His activism on apartheid led to him being arrested in 1984. He faced the death penalty for treason with twenty-one other political leaders in the 'Delmas Treason Trial'.
Simon came out to his co-defendants and a number of them thought that the state would use Simon’s being gay to undermine the moral stance of the anti-apartheid movement. In the end, his co-defendants accepted Simon’s argument that discrimination based on sexual orientation was just as unacceptable as racism.
His coming out to the men he went to jail with and who would go on to lead in the country has been of great importance for the development of LGBT rights in South Africa.
After leaving jail he observed:
He founded the Gay and Lesbian Organisation of the Witwatersrand in 1988. He traveled widely and was given several human rights awards in Europe and North America. He was a member of International Lesbian and Gay Association board, representing the African region.
Nkoli founded South Africa’s first AIDS advocacy groups, Township AIDS Project and the Gay Men’s Health Forum.
Steven Cohen wrote in 1998 that Nkoli "unified the black and white gay communities, ending faggot apartheid."
That constitution, in a world first, included 'sexual orientation' as protected against discrimination.
Patrick “Terror” Lekota, jailed with Nkoli and who became South Africa’s minister of defense, highlighted Nkoli’s contribution to the new constitution:
After becoming one of the first publicly HIV-positive African gay men, he initiated the Positive African Men group based in central Johannesburg. He had been infected with HIV for around 12 years, and had been seriously ill, on and off, for the last four. He died of AIDS in 1998 in Johannesburg.
Amongst numerous honors, he was made a freeman of New York by mayor David Dinkins in 1996. In 1999 the City of Johannesburg created 'Simon Nkoli Corner' on the junction of Hillbrow's Twist and Pretoria streets.
Canadian filmmaker John Greyson made a short film about Nkoli titled "A Moffie Called Simon" in 1987. Nkoli was the subject of Robert Colman's 2003 play, "Your Loving Simon", based on his prison letters (I was one of many around the world who corresponded with Simon), and Beverley Ditsie made a film in 2002 called "Simon & I".
Human rights campaigner Peter Tatchell worked with him in the 1980s. He said: