Sir Roger Douglas is promising to "do heaps" in Parliament even if it is from the back benches and has singled out primary school education as one of his first "projects".
Act candidate Sir Roger said that if elected he would do whatever he could to influence a National-led government if its leader, John Key, was true to his word and kept him out of a ministerial post.
"There's absolutely no way I'm going to sit around and do nothing - I'm going to do heaps.
"I will do a monthly project, I'll look at the big issues and I'll be outspoken - what else would you expect?"
Sir Roger, 70, said he would work on an issue like primary education "and if it gets a bit of mileage and support, people are forced to look at it, aren't they?"
He would try to drum up support for his projects from the media and the public.
Sir Roger said National "needs some backbone - and that's what I'm going to do".
Sir Roger is number three on Act's party list, and with leader Rodney Hide likely to win Epsom, he could be returned to Parliament after an absence of 18 years if the party gets 3 per cent of the vote.
National and Act have agreed to go into coalition but Mr Key has ruled Sir Roger out as a minister either in or outside the Cabinet.
Sir Roger said if Act did well, such as six or seven seats, then Mr Key would have to revisit his position.
Sir Roger, who was responsible for free market economic reform while a Labour Minister of Finance from 1984-88, said another one of his monthly projects could be healthcare.
He said he was not perturbed by Prime Minister Helen Clark's repeated criticism of his possible role in a National-led government.
"She probably thinks its good politics. We never did see eye to eye in the Labour Party."