Former National leader Don Brash has rejected an approach by ACT to stand for the party at this year's election.
It was reported ACT leader Rodney Hide approached Dr Brash in January.
The party's founder Roger Douglas, who has returned to ACT to stand as a candidate at the election, has said he also talked to Dr Brash.
But Dr Brash said he was not interested in returning to politics.
"I made it clear that I was not standing for any political party. I had four and a half years of Parliament -- it was a fantastic opportunity and for more than three years I was leader of the National Party," he told the Dominion Post newspaper.
"We made a substantial amount of progress in rebuilding support ... John Key is the new leader and I think he is doing a great job so no, I don't want to get back into Parliament."
Dr Brash was once described as ACT's "tenth MP" due to his hardline positions on many policy issues.
Wooing him to ACT would have been a significant boost for the party, potentially slicing off some of National's support at the far right end of the political spectrum.
In the past fortnight ACT has made the most of the return of Sir Roger, shopping the former finance minister around Wellington to highlight its free-market agenda.
NZPA