Sir Reg Empey was speaking after being confirmed as an election candidate in South Antrim
Sir Reg Empey has said he would resign from the assembly and as employment minister if he won the South Antrim seat in the general election.
The Ulster Unionist leader confirmed he will stand in the constituency after the rejection of the local party's preferred candidate - Adrian Watson.
Sir Reg received the unanimous backing of the local constituency association on Wednesday evening.
He had been expected not to stand in the general election.
"What has happened is things have changed," Sir Reg said on Thursday morning.
"First of all every other party leader is now fighting in the Westminster election and it's extremely difficult to put your case if you're not in the race.
"Secondly, I believe the project we have here is so important for Northern Ireland, to its future, to being a real meaningful part of the union, that I think it is important now to take a lead and give a lead
"Therefore I feel that the only place I can do that is to actually be in the campaign and participating in it."
William McCrea, who is the sitting MP, re-took the South Antrim seat for the DUP in 2005 with a majority of 3,448.
He said the DUP would have a greater influence than the Ulster Unionists should there be a "hung parliament".
"I believe that we as the DUP - not tied to any of the parties - can go in there and bat for Northern Ireland in a hung parliament situation," he said.
"Remember this, that is what all the political thinkers are saying, there will be a hung parliament."
Other candidates declared for south Antrim in 2010 are Alan Lawther of Alliance, Mel Lucas of the TUV, Thomas Burns of the SDLP and Sinn Fein's Mitchell McLaughlin.
Sir Reg succeeded David Trimble as Ulster Unionist leader in June 2005.
The mayor of Antrim, Adrian Watson, had originally been selected as the party's candidate in South Antrim by the local Ulster Unionist association.
However, the Conservatives - who have an electoral pact with the Ulster Unionists - raised objections and he was rejected by a joint committee of the two parties.
BBC NI political correspondent Gareth Gordon, said Sir Reg, who stood in East Belfast in the last general election, had been due to step aside this time to concentrate on assembly work and his job as employment and learning minister.
"However the void in South Antrim, which the party sees as one of its main target seats, has proved too tempting," he said.
"It's an opportunity, but also a gamble - Sir Reg Empey is effectively staking his political future and his position as party leader.
"The contest between the sitting MP William McCrea - who had a majority of about 3,500 last time around - and Sir Reg will be one of the highlights of the election."
'Slap in the face'
Alan Lawther of the Alliance Party said Sir Reg's decision to stand in South Antrim was "bizarre" and required "some explanation".
"This could be Reg's last throw of the dice as UUP leader, and it could be very embarrassing for him," he said.
"He is supposed to previously have expressed an interest in North Down and South Belfast. Why and how has he suddenly found a connection to South Antrim?"
Sinn Fein's Mitchell McLaughlin said the vote would be a verdict on Sir Reg's leadership.
"Reg's late entry into this contest is just further evidence of the disarray in the Unionist Party, not just in South Antrim but throughout the north.
"But his decision to fight the South Antrim seat will give the voters the opportunity to give their verdict on which party is providing strong, positive leadership."
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