Key Points:

Don Brash has resigned from Parliament, saying he believed he had helped bring more maturity to debates on economic and Maori affairs.

In the end, a week was a long time in politics for Dr Brash.

Last Thursday, Dr Brash called a press conference to resign from the leadership of the National Party.

A week later, he was back before a press conference announcing he was gone for good.

Dr Brash said today he had talked to friends, colleagues and family members, and decided it was the right time to leave Parliament.

He said he would stay on as an MP for a few weeks, but would not return to Parliament in the new year.

Dr Brash is a list MP. He will be replaced by the next candidate on National's list, Katrina Shanks. He has been an MP for five years.

At a press conference attended by fewer political journalists than for his resignation last week as leader of National, he said: "Over the last few days I've been considering my future in Parliament and have been talking with my wife, my wider family, my friends and my colleagues.

"I've come to the conclusion that now is the right time for me to leave Parliament and I informed (new leader) John Key of that earlier today."

Dr Brash said he intended to continue as an MP for a few more weeks to tie up loose ends.

"I entered Parliament in 2002 with the intention of making a difference and I leave believing that I've done that. The National Party is in great shape to win the next election and I believe that debate about economic policy and about the Treaty is more mature and more realistic than it was five years ago."

He said that the book by researcher, Nicky Hager, The Hollow Men, which detailed his links with the Exclusive Brethren, was not a factor in his resignation.

He had "constructive" meetings with Mr Key on Tuesday and again this morning but had decided to leave. He would not say whether he had sought a specific portfolio, like the Finance spokesmanship, in his discussions.

Asked whether he would look at directorships of companies, Dr Brash said he would. But asked if they might include directorships of SOEs, he replied "not with this Government".

He had consulted colleagues and their advice had been mixed. Some said, "you've done a fantastic job for the National Party. You're work on that has finished", said Dr Brash.