South African Archbishop Desmond Tutu on Thursday was awarded a one-off million-dollar prize by the Mo Ibrahim foundation that promotes good governance on the continent.

At a glitzy Johannesburg hotel, Sudanese-born billionaire Mo Ibrahim said the special civil society prize was in recognition of Tutu's "lifelong commitment to speaking truth to power."

He said the award was not designed to replace his annual excellence in African leadership prize, given to former heads of state who recently stepped down after a tenure that respected their country's constitution.

Ibrahim's prize giving has put him at front and centre of the debate over governance in Africa

Since 2006 the telecoms mogul's foundation has tried to give one African an initial prize of $5 million and an additional $200,00 a year for life.

But thanks to stringent criteria, he has not always been successful.

In the seven years since its inception, the annual prize has been awarded only three times, plus a special award for Nelson Mandela.

The award is given to a "democratically elected African head of state or government who has demonstrated exceptional leadership, served his or her constitutionally mandated term and left office in the last three years."

Previous winners of the multi-million dollar award include former presidents Joaquim Chissano of Mozambique, Festus Mogae of Botswana and Pedro Pires of Cape Verde.

In 2009 and 2010 the foundation did not award the prize, saying there were no suitable candidates.

The 2012 winner -- or lack of winner -- will be unveiled on October 12 in London.

The foundation also publishes an index of African Governance, which ranks countries on good governance.

Last year, Mauritius was at the top of the index, while Chad, Zimbabwe, the Democratic Republic of Congo and Central African Republic languished at the bottom.