The gaffe-prone leader of New Zealand's main opposition party resigned on Thursday, citing the destabilising effects of continuing leadership speculation.
Don Brash, 66, had led the conservative National Party for three years and came close to ending the six-year hold on power of Prime Minister Helen Clark's centre-left Labour Party in elections last year.
But Brash, who has been accused of an extra-marital affair and has been criticised after a number of faux pas, said there had been a growing expectation he would step down ahead of the next election due in 2008.
"That ongoing speculation is damaging to the National Party, and to our future prospects," Brash told a press conference.
"Accordingly, as we approach the end of the parliamentary year, I've decided to resign as leader with effect from a special caucus meeting which I'll call for early next week."
Brash's likely successor will be the party's finance spokesman, John Key, who confirmed he would stand for the leadership.
"I think I can bring to the job a fresh new dynamic and aspirational leadership for the party," Key said on Thursday.
Brash, a former central bank governor with a reputation as a hardline economic rationalist, only entered politics in 2002 and his relative lack of experience frequently raised questions about his political judgment.
Under his leadership, the National Party increased its number of seats in the 2005 election from 27 to 48 with his lack of a slick political persona appealing to many voters.