Varadkar, 38, will officially take over as Taoiseach, as the Irish prime ministerial title is known in Ireland, in Parliament later this month after he was declared the winner in the leadership race for the Fine Gael party.
He took a majority of the votes to be declared as the 11th leader of the party as counting concluded at Mansion House in Dublin.
The final count, including all three electoral colleges, saw Varadkar win with 60 per cent to Housing Minister Simon Coveney's 40 per cent votes.
Polling had closed earlier on Friday with a 100 per cent turnout in the parliamentary party recorded.
The Dublin-born son of Mumbai-born Ashok Varadkar and Irish mother Miriam, served as Ireland's welfare minister and had emerged as the most popular choice since he announced his candidacy after current leader Enda Kenny stepped down as prime minister earlier this year.
Varadkar went up against housing minister Coveney in the leadership race, who bagged two-thirds of the party membership votes but lost out to the more popular candidate in the end.
The voting for the Fine Gael leadership is decided in an electoral college system that gives the Fine Gael parliamentary party 65 per cent of the vote. The 21,000 rank-and-file members of the party have 25 per cent and 235 local representatives 10 per cent.
The parliamentary party voted for Varadkar, overwhelmingly, as was widely expected.
Ireland's new Taoiseach is expected to be formally confirmed by June 13, when the country's Dail Parliament resumes following a week-long break.
Varadkar came out as a gay man in 2015, when Ireland became the first country in the world to legalise same-sex marriage through popular vote.
In a coming-out speech he gave in a radio interview, he had said, "It's not something that defines me. I'm not a half-Indian politician, or a doctor politician or a gay politician for that matter. It's just part of who I am, it doesn't define me, it is part of my character I suppose."
His family originates from Varad region near Malwan along Maharashtra's Konkan coast, and Leo Varadkar kept his Indian connect alive, completing an internship at the King Edward Memorial Hospital in Mumbai.
His partner, Matthew Barrett, is also a doctor.
"Matt is just a very special person. Someone who is unconditionally on my side, which is always great. He is the kind of person who has made me a better person," Varadkar recently said.
The popular minister has campaigned for same-sex marriage and liberalising abortion laws.
He worked as a general practitioner before winning a seat in Parliament in 2007 and has rapidly risen through the party ranks, holding several ministerial portfolios including minister for social protection and minister for transport, tourism and sports.
Fine Gael is Ireland's centre-right political party, seen as taking liberal positions on several social and economic issues. Varadkar was campaigning on a platform of reducing child poverty and educational disadvantage as key policy areas.
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