The former GP, who came out as gay in 2015, is confirmed as taoiseach in Dil ceremony in Dublin
The son of an Indian immigrant has made Irish history by becoming the countrys youngest and first openly gay prime minister.
Leo Varadkar, 38, was formally elected taoiseach at a confirmation ceremony in the Dil in Dublin after he won the Fine Gael party leadership earlier this month. Enda Kenny, who stepped down after six years, said his successor represented a modest, diverse and inclusive Ireland.
The former GP, son of an Indian father and Irish mother, faces a number of challenges as he takes over the only EU country that has a land border with the UK as it prepares for Brexit. The country may experience an impact on prosperity and trade across the open border as it works towards restoring a power-sharing government in Northern Ireland.
Abortion will be another big issue for Varadkar, specifically demands for a referendum on the future of the eighth amendment of Irelands constitution.
Pro-choice reformers say the country cannot liberalise its strict anti-abortion law until the eighth amendment, which gives equal citizenship to the foetus in the womb, is abolished, but a second referendum would be needed.
One of the first world leaders Varadkar planned to call after being appointed taoiseach was Theresa May, when he would convey the sympathy of the Irish people over the loss of life in the fire at Grenfell Tower in west London.
In his first speech as taoiseach, Varadkar told the Dil: The UK has been through some terrible tragedies over the past few weeks so we offer them our sympathy and solidarity.