Mmusi Maimane on Thursday resigned as a member of the Democratic Alliance, as an MP and its parliamentary leader, a day after quitting as leader of the official opposition party.
Maimane announced his resignation from all party structures on Twitter and a senior member of the party confirmed the move.
He resigned after four years at the helm of the DA, saying on Wednesday he was no longer convinced that it was the best vehicle for realising his vision of a united and reconciled South Africa.
In a double blow for the party, Athol Trollip also quit his post of federal chairman.
There have been rumblings for months about Maimane's future in the DA following the party's poor showing in the May national elections. It shed 1.5 percent of its voter support.
But Maimane took the plunge after his former mentor and predecessor as DA leader, Helen Zille, returned from political retirement at the weekend to take up the key position of chairwoman of the party's federal council.
I have worked tirelessly to build the project of One SA for All. It’s been my greatest honour to serve the people of SA and will continue to do so. I have today resigned from the DA and Parliament. Thank you to the people of this country for your faith in our nation. God bless SA
— Mmusi Maimane (@MmusiMaimane) October 24, 2019
The departure of both Maimane and Trollip have left the DA without a leader as, in terms of its rules, the federal chairperson would step into the breech if the party leader resigns.
With both gone, Zille said the DA was consulting lawyers on how to proceed to fill Maimane's shoes until the party could formally elect a new leader.
On Wednesday, Maimane had said there was a sustained effort from a faction within the party to undermine him.
He also aimed a swipe at Zille, saying though their mutual respect remained intact, she had damaged the party with her controversial remarks in 2016 on the legacy of colonialism.
But his opponents within the party have quietly said for months that Maimane had failed to broaden the party's support base and shown himself to be weak on policy matters, and should therefore take the fall for its disappointing performance in the elections.