New Ulster Unionist leader Tom Elliott will meet party staff and officers following his landslide victory.
Congratulations poured in from across the political spectrum after the Co Fermanagh farmer, 46, saw off the challenge of Lagan Valley Assembly member Basil McCrea by 643 votes to 294. Members gathered in Belfast to cast their vote.
Sir Reg Empey had announced he would quit as Ulster Unionist leader following a dismal general election which left it with no MPs.
Many of the party's senior figures including all but one of its Assembly members had declared their backing for Mr Elliott.
He told the meeting: "We cannot become the leading party in unionism again without unanimity."
He added: "My focus has not been on tonight, it has been on tomorrow and thereafter and that is what is important."
Mr Elliot, a senior Orangeman and former Ulster Defence Regiment soldier from Ballinamallard, paid tribute to his opponent and said the party was a broad church.
He said: "I will certainly not make this a cold house, a cold party for you and your colleagues."
The 14th leader said his party needs to be united and build ahead of next year's assembly elections.
"What I want for the Ulster Unionist Party is the very same thing I want for Northern Ireland; I want people with a settled mindset to live in comfort and peace within this province and within the union," he told journalists following the vote.