A breakaway faction of South Africa's governing African National Congress (ANC) is due to register as a party.
The South African Democratic Congress is formed from ex-ANC members who left the party after former President Thabo Mbeki stepped down in September.
At a national convention at the weekend the new party accused the ANC of undermining South Africa's democracy.
ANC leader Jacob Zuma has said he was confident his party would win next year's elections.
The South African Democratic Congress (SADC) is being led by Mosiuoa Lekota, the former defence minister and ANC chairman.
His deputy will be Mbhazima Shilowa, the former premier of Gauteng Province.
The SADC is expected to officially register as a party with the Independent Electoral Commission on Monday.
'Engage in debate'
Mr Zuma questioned the motives of the ANC dissidents forming the new party and called them "bigamists" for seeking to join up with opposition parties so soon after leaving the ANC.
"Even before the divorce has concluded they have now announced that they will be getting married to the Democratic Alliance and other opposition parties to form a coalition," the South African Press Association quoted Mr Zuma as saying.
But he told a rally of thousands of people in Soweto the ANC was looking to the faction forming a party "so that we can engage them in debate, not in anger".
"The ANC is still the party it was in the old days," he said. "We are going to win the upcoming election with an overwhelming majority, as we have done in previous years."
Meanwhile, the SADC leaders have said they "do not underestimate the work that lies ahead" as they seek to win the election next year.
"We want to become the next government in the provinces and at the national level. We want to be in the majority," Mr Shilowa told reporters.
Mr Shilowa told the Sunday Independent newspaper that his faction were "not doing this just to be another opposition".
"It is about believing in ourselves and about South Africans believing that this new formation we are going to put in place will contest for political power, not just participate in the elections," he said.
On Saturday, more than 6,000 delegates attended a conference in Johannesburg to discuss establishing the party.
SADC's leader, Mosiuoa Lekota, accused the ANC of abusing its power for personal gain and said his group was "ready to fight as messengers and representatives of hope for the people".
The party's launch means that the campaigning for next year's elections has already begun, though it is unclear whether SADC's policies will be significantly different from those of the ANC.
The infighting stems from a power struggle between former president Thabo Mbeki and Jacob Zuma, who defeated Mr Mbeki to become party leader last December.
Mr Mbeki stood down in September after a judge suggested he may have interfered in the prosecution of Mr Zuma on corruption charges. Mr Mbeki strongly denies the claim.
His ousting led ex-defence minister Mosiuoa Lekota and other loyalists to quit the ANC in protest.
Mr Lekota officially resigned from the party on Friday.
The disaffected ANC members accuse the party of undermining South Africa's young democracy.
The political schism marks a dramatic shake-up in a country where the ANC has dominated political life since the end of white-minority rule in 1994.
The ANC won more than two-thirds of votes in the last election and controls a strong majority in parliament.