The new Alliance leader, Mr David Ford, said his party has a radical vision for a better society and has an important role to play in the future of Northern Ireland.
He was speaking after he defeated the party's deputy leader, Ms Eileen Bell, by 86 votes to 45 for the leadership at a special party council meeting on Saturday. Alliance has suffered a dramatic electoral decline in recent years.
It won only 5 per cent of the vote in June's local government elections. In its heyday, during the 1974 district council elections, Alliance secured 14.4 per cent support.
Mr Ford said: "No doubt there is a role for Alliance in the future, a different, clear, radical vision of a better Northern Ireland than what we have at the moment.
"There are a lot of people out there at the moment who want us to be their representatives and need us to be their representatives."
Mr Ford said he would set out his new vision for the North at the party conference at Stormont later this month.
Mr Ford (50), who resigned as the party's chief whip in August, has been an Assembly member for South Antrim since 1998. He is a former chairman of the Northern Ireland branch of the Liberal Democrats. He joined Alliance at its foundation in 1970 and is a former party general secretary. He took part in the negotiations for the Belfast Agreement.