Dr. Ramphele has been a fixture in South African public life for decades. She had a close relationship with the Black Consciousness activist Steve Biko, who died in police custody in 1977, having two children with him. The apartheid government banished her for seven years to the village of Lenyenye, in a bleak northern corner of the country, for her political activism. Undeterred, she started a small clinic that treated thousands of rural residents. She also earned degrees in anthropology and business.

When apartheid ended, she was named vice chancellor of the University of Cape Town, the first black person to hold the post. She later became a managing director of the World Bank, and in recent years she has been sought after as a corporate board member.

Though her career has given her sterling international credentials, it remains to be seen whether she can muster a mass following in a country where populist appeal has proved essential to political success. Asked about the size of her team, she responded that “we are an energetic team of five.” Hobnobbing with corporate titans and global leaders has left Dr. Ramphele open to charges of elitism, some say.

Bantu Holomisa, the leader of the United Democratic Movement, which he started after leaving the A.N.C. in 1997, said in a statement that he welcomed Dr. Ramphele to politics and signaled a willingness to join forces.

“We look forward to working with Dr. Ramphele in our efforts to build a strong political alternative for the people of South Africa,” he said.

But efforts to blunt A.N.C. dominance have struggled in the past. The Congress of the People, a breakaway party started in 2008 by supporters of former President Thabo Mbeki and other disgruntled A.N.C. members, has had its power wane.

The A.N.C. has been rocked by scandal and tragedy over the past year. President Jacob Zuma has faced repeated investigations over $27 million in government money spent on security upgrades to his private residence in his home village of Nkandla. The killing of 33 striking workers by the police at a platinum mine in August caused many to question the A.N.C.’s commitment to helping the poor. The crisis led credit agencies to slash the country’s debt rating, which has hurt economic growth.