Tens of thousands of people cheered as William Ruto was sworn in as Kenya’s president at a ceremony in the capital Nairobi following his narrow election win last month.
Mr Ruto hailed it as “a moment like no other”, adding that a “village boy” had become president.
Defeated candidate Raila Odinga did not attend. He said he had “serious concerns” about his opponent’s victory.
Mr Ruto won the election with 50.5% of the vote, to Mr Odinga’s 48.8%.
Mr Odinga has alleged that the result was rigged, but the Supreme Court has ruled the election was free and fair.
Mr Ruto – the former deputy president – was handed a copy of Kenya’s constitution and a sword to represent the transfer of power.
With his hand on a Bible, the 55-year-old swore to preserve and protect the constitution.
“Standing here today is testimony that there is God in heaven. I want to thank God because a village boy has become the president of Kenya,” Mr Ruto said, referring to the fact that he grew up in rural Kenya.
He also had conciliatory words for his rival, Raila Odinga, and supporters of his opponents: “Their supporters will be my constituents. I will work with all Kenyans irrespective of who they voted for”, he said.
He said the Ruto administration marked “freedom” for Kenya, and the days when people were targeted because of their association with him “are over.”
Earlier, at least eight people were reported to have been injured in a crush as they jostled to enter the stadium to witness the ceremony.
But inside the stadium the crowd was in high-sprits, with frequent cheering, waiving of the Kenyan flag, and groups of people proudly wearing yellow – the colour synonymous with Mr Ruto’s campaign.
There was also a handshake between outgoing President Uhuru Kenyatta and Mr Ruto, his former deputy with whom he fell out during their second term in office.
Religion was a persistent theme throughout the swearing in ceremony, with leaders from the Christian and Islamic faiths offering prayers for the new president.
Bishop Mark Kariuki said God had showcased his might by elevating Mr Ruto, who was once a road-side chicken seller, to the presidency.