Nosimo Balindlela and her husband Miniyakhe.
"Today, on behalf of the DA, I am delighted to welcome Nosimo Balindlela into our ranks," Zille said in a statement.
Balindlela resigned her Cope membership and her seat in the National Assembly.
She would sign a Democratic Alliance membership form and receive her membership card from DA Eastern Cape provincial leader, Athol Trollip.
Zille said she had known Balindlela for many years "as a person of integrity". It was clear "she is someone with the core values that will take this country forward".
Zille said there were many South Africans like Balindlela frustrated by present divisions, and who understood the future lay in transcending "obsolete political formations".
She described Balindlela's move as a step in the realignment of politics in South Africa, and invited others like her to join the DA.
Building a non-racial majority
Balindlela was an ANC-appointed premier of the Eastern Cape from 2004 to 2008 before she was removed by the party. She had heard rumours this was about to happen while on an official visit to China.
In an interview at the time, she told Sapa that ANC secretary general Gwede Mantashe said she was fired over a lack of service delivery.
Balindlela later joined the Congress of the People, formed by a group which broke away from the ANC when former president Thabo Mbeki was removed as party leader.
Balindlela is a teacher by profession who first because involved in the struggle against apartheid at the University of Fort Hare.
She was a prominent United Democratic Front activist in the 1980s, and in 1994 was elected to the Eastern Cape legislature, where she was appointed provincial minister for education, sports and culture.
She served on the provincial executive committee of the ANC from 1996 to 2008, the provincial working committee from 2004 to 2008, and was the provincial chairperson of the ANC Women's League from 1996 to 2001, according to a DA-supplied biography.
Zille said the DA was working hard to build a new, non-racial majority at the centre of South African politics that all voters could trust. – Sapa