Zimbabwe's President Robert Mugabe is to face two Movement for Democratic Change opponents in presidential polls.
Mr Tsvangirai will run again against Robert Mugabe
Both MDC factions said they would take part in the 29 March election - but talks on uniting behind main leader, Morgan Tsvangirai broke down on Sunday.
The two wings split in 2005. Rival MDC Arthur Mutambara head said the talks had broken down irretrievably.
"People of Zimbabwe, we apologise for failing to construct a united front," he told reporters.
He admitted the opposition's chances of winning had been sharply reduced.
Mr Tsvangirai, leader of the larger MDC faction, confirmed the disagreement at a separate news conference.
"We can't force it [unity] down the people's throat. It's regrettable, it's unfortunate, but that's the reality."
The opposition are still demanding a new constitution but say they will field separate candidates in presidential, parliamentary and local elections.
Mr Mugabe defeated Mr Tsvangirai in 2002 elections, which were criticised by election observers.
"We are giving the people of Zimbabwe a fighting chance against the dictatorship," Mr Tsvangirai said.
"We aim to focus on Robert Mugabe and Zanu-PF as the authors of the present national crisis."
Zimbabwe is in the midst of an economic meltdown, which Mr Mugabe's critics blame on his seizure of white-owned farms.
He says he is the victim of an international plot intended to bring him down.
Zimbabwe has the world's highest rate of annual inflation - 26,000% - while just one in five has an official job.