The Democratic Alliance announced the defection of Nosimo Balindlela, formerly of the ANC’s top council.
Balindlela was also head of the Eastern Cape’s provincial government, an ANC stronghold and the home of Nelson Mandela.
“I have taken this step because I do believe the DA is the future,” Balindlela told reporters.
Evoking the names of ANC giants Oliver Tambo and Mandela, she told journalists that South Africa was not the country they had imagined.
“This is not what they wanted us to be. They wanted to make sure that racism is finished in South Africa and it is very sad that we are still on that tag of racism.”
While Balindlela is no longer considered a major player in South African politics, her defection will be a blow to the already underfire ANC.
It will also provide a boost to the Democratic Alliance, which has sometimes struggled to win over black voters.
Balindlela was pushed from her post as Eastern Cape leader in 2008 after her province opposed Jacob Zuma’s successful bid to oust Thabo Mbeki from the presidency.
She later joined the Congress of the People that split from the ANC four years ago.
DA leader Helen Zille lauded the move.
“Many of us understand that our future lies in transcending these obsolete political formations. But it takes a courageous person to be among the first to show the way to others.”