Niger has a democratic transfer of power after Mohamed Bazoum was sworn in as president.
It comes just days after the government says it thwarted an attempted coup by parts of the military.
The West African nation is facing increasing attacks by jihadist groups and political tensions in the country since the election in February.
The inauguration marks the first time one elected leader has handed power to another since independence in 1960.
There was tight security in the capital, Niamey, ahead of the ceremony, two days after soldiers opened fire on the presidential palace in a foiled coup attempt.
The government said security forces arrested several people connected to the coup on Wednesday.
Niger is the world’s poorest nation, according to the UN’s development rankings for 189 countries. It has seen four military coups, most recently in 2010.
Who is Niger’s new president?
Mr Bazoum, 61, a former interior minister, won over half the share of the vote in an election in February.
But Mr Bazoum’s main rival, Mahamane Ousmane, rejected the election result and claimed there was fraud. His supporters have held mass rallies and violence has increased since the election.
Mr Bazoum succeeds Mahamadou Issoufou, who has stepped down after a decade in power. Last month, the outgoing president was awarded a $5m (£3.6m) leadership prize – which he could only receive if he left office.
Among President Bazoum’s top priorities will be tackling a deadly Islamist insurgency in the west of the country.
Niger has seen an upsurge in suspected jihadist violence, with an estimated 300 people dying this year in attacks.
Last month Niger saw the worst militant attack in its history, when suspected jihadists raided several villages, killing 137 people.