Don Brash will resign to the Act Board tomorrow after it became clear that he would not get back into Parliament.
His party has failed to secure enough party votes to get more than one MP. Epsom candidate
John Banks won his seat and will return to Parliament as the party's only representative.
Tonight Don Brash thanked his party's supporters.
"Despite all the commentators, all the polls, all the media, we did it. You did it, John Banks did it, the people of Epsom did it.
"I want to thanks John Banks, he did a fantastic job."
Earlier on TVNZ, former Act MP Deborah Coddington asked the question that almost all Act supporters must be asking of Don Brash.
"Where the 15 per cent, Don?"
Don Brash replaced Rodney Hide as leader, promising to resurrect the fortunes of the party to grab 15 per cent of the vote.
Instead, it has one MP, John Banks in Epsom, and barely one per cent of the total vote.
Asked about the Act performance, Ms Coddington was blunt.
"It's appalling. Where's the 15 per cent Don?"
Quizzed on TVNZ's Election Special about when Mr Brash might face a leadership challenge, Ms Coddington replied "When's lunch?"
She said that John Banks should stay out of Cabinet in a National-led government and concentrate instead on rebuilding the party.