Ashraf Ghani has been sworn in as Afghanistan's president in a ceremony at the presidential palace in Kabul, the BBC reported Monday.
It comes after six months of deadlock amid a bitter dispute over electoral fraud and a recount of votes.
Under a US-brokered unity deal, Ghani takes over the presidency and runner-up Abdullah Abdullah can nominate a figure with prime-ministerial powers.
The Taliban have described the deal as a "US-orchestrated sham" but Ghani hailed it as a "big victory".
Ghani took an oath to abide by the constitution at the swearing-in ceremony attended by up to 100 dignitaries.
He has praised the country's "first democratic transfer of power" and has also spoken warmly of his rival, and now partner in government, Abdullah.
Abdullah, who takes on the newly created role of chief executive, said the two leaders would work together "for a better future with trust and honesty".