The Ulster Unionist Party has agreed to form an electoral pact with the Conservatives.
The deal will initially see the parties run on a joint ticket in Westminster and European elections in Northern Ireland.
Representatives from both parties will form a joint committee to work out on cooperation and an electoral strategy.
A UUP spokesman said its executive committee had "overwhelmingly endorsed" the decision.
The Conservative Party has just one councillor in Northern Ireland, however, Down District Council's Peter Bowles is yet to stand for election under the Tory banner.
Mr Bowles defected to the Conservative Party in 2006 in protest at the UUP's assembly links with the late David Ervine, who was leader of the UVF-linked Progressive Unionist Party.