LADY Sylvia Hermon has announced her intention to run as an independent in the forthcoming election.
The confirmation by the North Down MP follows weeks of intense speculation about her political future.
In a statement, Lady Hermon revealed her resignation from the Ulster Unionist Party came into effect from midnight on Wednesday.
The party's former sole MP has left the party in protest at its electoral link-up with the Conservative Party for the Westminster poll, expected in May.
However, Ms Hermon said leaving the UUP caused her "profound sadness".
"As we approach the end of this Parliament with the Easter Recess beginning next Tuesday and dissolution expected shortly thereafter, the mandate given to me at the last General Election to serve the people of North Down as an Ulster Unionist is virtually at an end," she said.
"The distance, however, between me and my Party has become so great over recent months that I have decided to resign from the Ulster Unionist Party with effect from midnight last night (Wednesday).
"I have taken a considerable amount of time to think and to reflect before coming to this decision, but I believe it to be the right one for the Party and for me."
She added: "It is now my intention to stand my ground, fighting the forthcoming General Election as an independent and fighting to win.
"The tremendous support I have received from constituents during the recent stressful and difficult time in my political life has encouraged me greatly, and convinced me that I ought to run again as a candidate.
UUP leader Sir Reg Empey expressed his "deep regret" at Lady Hermon's decision.
He said: "I wish to thank her for her contribution to Ulster Unionism since her election in 2001. I believe that the values we share far outweigh the differences in approach to some issues.
"The Party's major policy decisions have been reached after widespread consultation and have been unanimous."
"I wish Lady Sylvia and her family well in the future," Sir Reg added.
At the weekend, Ian Parsley was selected as the joint UUP-Conservative candidate for the constituency.
There is also growing speculation that the DUP will not stand in the Westminster election in North Down.