Agang, which means “Build”, has made tackling corruption and improving education two of its main goals.
Its leader, Mamphela Ramphele, told supporters in Pretoria the ANC could not be trusted to run the economy.
Ms Ramphele is a former World Bank managing director and was the partner of murdered anti-apartheid activist Steve Biko.
Ahead of Saturday’s launch, retired Archbishop Desmond Tutu described her as a brave and principled leader and said the graciousness of South African politics in the 1990s had largely been surrendered at the altar of power and wealth.
“Few thinking South Africans would not welcome the entry into South African politics of someone of the calibre, background, intellect and resourcefulness of Mamphela Ramphele,” he said in a statement.
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We are not bringing any baggage to the party”
Mamphela Ramphele
The BBC’s Karen Allen in Johannesburg says the ANC is regularly accused of poor governance and failing to deliver basic services such as housing, water and jobs.
Agang’s stated aim, she says, is to galvanise South Africans to build on the democratic foundations left by former President Nelson Mandela and other anti-apartheid leaders – a legacy which some believe is being squandered by the ANC.
However, loyalty to the ANC among South African voters runs deep, our correspondent adds.
Coalition possible
Ms Ramphele has spoken about the possibility of forging coalitions with other parties, and analysts say the most obvious candidate is the Democratic Alliance (DA), South Africa’s official opposition.
She told the BBC that her party was still “in conversation” with the DA but added: “We can reach much further than where the DA can reach, because we are not bringing any baggage to the party.”
When Ms Ramphele first unveiled her new party earlier this year she said she was seeking to end ANC rule.
“Corruption, nepotism and patronage have become the hallmarks of the conduct of many in public service,” she said.
At the time, ANC spokesman Jackson Mthembu said his party believed Ms Ramphele was “grievance-driven” and had failed to offer solutions to South Africa’s problems.
The ANC will seek to extend its 19 years in power in elections next year.
The ANC won the 2009 election with 65.9% of the vote. A breakaway party, the Congress of the People (Cope), failed to make a significant impact, analysts say.