Leo Varadkar has been announced as the leader of the biggest party in Ireland's ruling coalition, Fine Gael.
Mr Varadkar beat his rival, Housing Minister Simon Coveney, with 60 percent of the votes. He will become Ireland's first gay taoiseach (prime minister).
He is expected to take over from former Fine Gael leader Enda Kenny in the next few weeks.
At 38, he will also be Ireland's youngest ever prime minister.
Following the announcement on Friday evening, Mr Varadkar said he was "honoured" to accept the "enormous challenge" ahead of him with humility.
"If my election shows anything it's that prejudice has no hold in this Republic," he said.
"When my father travelled 5000 miles to build a new home in Ireland, I doubt he ever dreamed his son would grow up to be its leader."
He said Simon Coveney had gained his and the party's admiration for his "principled and spirited" campaign and he looked forward to working with him to bring Fine Gael and Ireland forward.
"Let that be our mission, to build a republic of opportunity," he said.
The leadership was decided in an electoral college system that gave 65 percent of the vote to the Fine Gael parliamentary party - made up of 73 TDs (members of the Irish assembly), senators and MEPs.
The party's 21,000 rank-and-file members had 25 percent of the vote, and 235 local representatives had 10 percent.
Mr Varadkar, who came out as gay in the run up to the 2015 same-sex marriage referendum, has been in charge of the welfare system.
He has come to personify the liberalisation of a country which was once regarded as one of Europe's most socially conservative nations - homosexuality was illegal until 1993.
However, Mr Varadkar has come under criticism for his comments on progressive issues and workers' rights.
The new Fine Gael leader will have to be endorsed by the independent members of the minority coalition government before he becomes taoiseach. That's expected to happen later this month.
Enda Kenny, 66, who led the party for 15 years and was elected taoiseach in 2011, resigned as Fine Gael leader in May.
Voting took place this week around the country.