Tom Elliott has become the 14th leader of the Ulster Unionist Party.
The Co Fermanagh farmer, 46, represents Fermanagh and South Tyrone in the Northern Ireland Assembly and will take over from Sir Reg Empey with a promise to reconnect with party grassroots.
He defeated rival Basil McCrea, who represents Lagan Valley in the Assembly, by 643 votes to 294 following a party meeting in Belfast at which around 1,000 delegates gathered.
Mr Elliott said: "We cannot become the leading party in unionism again without unanimity."
He paid tribute to his opponent Mr McCrea, saying: "I will certainly not make this a cold house, a cold party for you and your colleagues."
The new leader will have to bring the party together after an at times acrimonious race.
He said his defeated opponent had at times annoyed him, but added: "Every member of this party, whatever wing they belong to, provided they support the basis, the principles, the ethos and policies of this party that is what is important."
Mr McCrea acknowledged the victor's campaign and said he was a wonderful person. "I wish him really well in the future," he added.
Mr Elliott will have to win back votes from the Democratic Unionist Party after a decade in which the UUP has gone from having 10 MPs to none.
He said the party's link-up with the Conservatives which failed to win a Westminster seat is at an end and added there will be no electoral pact with the DUP.