Doug Beattie has said the Alliance Party attracted voters away from “angry, negative unionism”.
The Ulster Unionist Party leader was elected in his Upper Bann constituency, despite fears he could lose his seat.
Mr Beattie, speaking after he arrived at the Magherafelt count centre alongside Foyle candidate Ryan McCready, admitted that it had been a battle: “I think you never take the electorate for granted.
“I am from Upper Bann, I have had to make unpopular decisions in the direction of the party as party leader and that may well have had an effect on me, but these are the sort of things you go through all the time when you’re thinking about an election.
“Angry negative unionism is turning people off,” he said.
“People are going to the likes of the Alliance Party in droves because they’re being turned off by that angry, negative unionism.
“It might take a while to change that psyche. It may well be a supertanker that has a large turning circle, but we need to do it.”
Mr Beattie said that the party had performed well in Foyle, Belfast and in North Antrim.
Mr McCready on Saturday was in a tough battle for the final seat in the Foyle constituency.
The Ulster Unionist leader was also asked about the future of his leadership.
“People can question my leadership all they want.
“I’ve set the direction of travel. And what we have done previously, within the Ulster Unionist Party, is something bad has happened and we’ve all said ‘Oh, we’ll have to rethink what we’re doing’ and we’ve gone off in a completely different direction.
“I don’t believe that’s the case this time.”
He said that his priority was getting the Executive restored.
“We need to be working for the people.
“So the Government needs to be up and running. That means getting the Executive up and running.
“That means people getting in and getting it working again, we need to be able to spend over £300 million that’s sitting there because people need it.”
Earlier, the Ulster Unionist Party’s Rosemary Barton, who is set to lose her seat in Fermanagh and South Tyrone to party colleague Tom Elliott, has said the UUP must not forget conservative voters.
Ms Barton said that what happens next is up to the party leader.
Her defeat leaves the party with no female MLAs.
“I’m not sure what has gone wrong, but I think we do need to, perhaps, look at the strategies we have for the future,” Ms Barton told the PA news agency.
“We have to be progressive but we also cannot forget about those that are slightly more conservative. They have got to be brought along also.
“That’s something that the party must be very mindful of.”
The Ulster Unionists also suffered a blow in East Antrim, where Roy Beggs Jr, a former Stormont deputy speaker and party stalwart, was eliminated early in the voting process for the constituency, which covers the coastal towns of Carrickfergus and Larne.
Mr Beggs had been his party’s longest serving MLA, having held the seat since 1998.