One of Kenya's main opposition parties, ODM-Kenya, has nominated former Foreign Minister Kalonzo Musyoka as its candidate for this year's elections.
Kalonzo Musyoka is running third in opinion polls
He is the first presidential candidate to be officially named.
Attempts to select a single opposition candidate failed and on Saturday another opposition presidential candidate is to be announced.
President Mwai Kibaki is expected to seek re-election but has not formally put his named forward yet.
The BBC's Adam Mynott in the capital, Nairobi, says election fever is beginning to infect the country.
Opposition politicians from all sides combined two years ago under the banner of the Orange Democratic Movement (ODM) to defeat a referendum on the government's proposed constitutional changes.
Our correspondent says the ODM presented a powerful political force, but since then the grouping has split completely, largely over who should be endorsed as presidential candidate.
At a sports stadium on the outskirts of Nairobi 3,500 members of one of the resulting splinter parties, ODM-Kenya, chose Mr Musyoka to run for the country's most powerful position.
"The next step... is to go around the country and seek the votes that will ensure we get into State House," Mr Musyoka told cheering supporters.
On Saturday, the ODM is to nominate its candidate.
Others are expected to declare in the coming days to make it a crowded race for Kenya's presidency, our correspondent says.
Reuters news agency reports that opinion polls show Mr Musyoka running third, behind Mr Kibaki and veteran politician Raila Odinga, from the ODM.