Mr Boesak denied 32 counts of fraud and theft of funds from the soft- drinks company Coca-Cola, Scandinavian donor agencies and the American singer Paul Simon. Mr Boesak's bookkeeper, Freddy Steenkamp, serving six years after pleading guilty to similar charges, is the prime prosecution witness.
Mr Steenkamp has accused Mr Boesak of collaborating with him in defrauding the Swedish International Development Agency, Danchurch Aid and other agencies that donated funds to Mr Boesak's Foundation for Peace and Justice.
After a year of delays, caused by wrangles over legal funds for his defence, Mr Boesak came to court, supported by his wife, Elna, and his children from a previous marriage. "I feel good. I've waited four years for this," Mr Boesak told journalists as he entered the court.
The accusations were first made by a Danish aid agency before South Africa's first fully democratic elections in 1994.
Mr Boesak's case was postponed several times due to a row with the Legal Aid Board over funding for his defence. Finally, a mystery benefactor has come forward to pay 1m rand to fund the expense of a whole legal team, not just senior counsel. The trial is expected to last three months.
A small group of African National Congress supporters, dressed in the black, green and yellow of the ruling ANC, carried signs reading: "Boesak we will stand by you." Millie Jacobs, wearing a Nelson Mandela T-shirt, told reporters outside the courthouse: "He's our comrade and we have to support him. If he goes to jail, we will all go with him."
The former cleric, who later entered party politics and became Western Cape leader of the ANC, says the delays have been agonising and he has been living off friends' charity.
Mr Boesak, 52, who models himself on Martin Luther King, was unabashed yesterday despite the accusations, including claims that he siphoned money from his charity to help his second wife, a former radio and television personality, set up her own communications business.
"We've been waiting for this day for years," he said. "It's been a long, dark haul."
Dawn King, a forensic accountant and investigator, was the first state witness to appear. Her testimony is likely to last for up to three weeks.
Prosecutors have not yet decided which other witnesses to call, but they could put the Nobel laureate Desmond Tutu, who is the former Archbishop of Cape Town, and other prominent anti-apartheid campaigners on the stand.
Mr Boesak, a one-time provincial leader of the ANC, lost his job as ambassador- designate to the United Nations in Geneva when the fraud accusations against him surfaced three years ago.
Yet he remains popular within the ANC and counts the Justice Minister, Dullah Omar, among his supporters.
Mr Boesak's high-profile case has dented foreign donor confidence in South Africa, already struggling to attract funds after charities shifted their focus from helping to fight the ravages of apartheid to aiding poorer African nations.Reuse content