The son of Kenya's first president has won the battle for control of the former ruling party, Kanu, amid allegations of rigging.
Uhuru Kenyatta lost the 2002 election
Uhuru Kenyatta polled 2,980 votes against 622 for Nicholas Biwott, one of Kenya's most powerful men during the time of ex-President Daniel arap Moi.
Mr Kenyatta, son of Jomo Kenyatta, succeeds Mr Moi, as leader of the party which ruled Kenya until 2002.
Mr Biwott said that unauthorised delegates had been allowed to vote.
He twice stormed out of the meeting, according to the AFP news agency.
Correspondents say the election of Mr Kenyatta, 43, marks a generation change at the top of Kenya's main opposition party.
"This is an opportunity to make change in the country," he said.
Mr Kenyatta was Kanu's presidential candidate in the 2002 election won by President Mwai Kibaki on an anti-corruption ticket.
Kanu governed Kenya for almost 40 years following independence.