The leader of South Africa's largest opposition party has stepped down.

Democratic Alliance leader Helen Zille announced on Sunday that she would not stand for re-election in the party's upcoming congress in May this year.

In a statement, Zille said she her decision to step down two years earlier than she had originally planned was in the best interest of the party.

Zille said she would remain the premier of South Africa's Western Cape province.

The party's former parliamentary leader and a favorite to succeed Zille, Lindiwe Mazibuko, said in a statement on Monday that she would not run for the party's top seat. Mazibuko is in the United States, studying at Harvard University.

The Democratic Alliance won 22 percent in South Africa's 2014 national election.