Departing Labour MP Clayton Cosgrove says he's leaving politics on his own terms.

A Labour MP since 1999, Mr Cosgrove won't stand for the party at next year's election.

He rejects any suggestion he's being forced out.

"Any journalist who attempts to contrive any deviousness or underlying messages about this decision is wrong."

He said his decision to stand down was "about new challenges and opportunities".

Leader Andrew Little backs that up.

"We're nowhere near putting our lists together for 2017. This is a decision of Clayton's and that's really all it is."

SEE ALSO: Cosgrove won't stand again

Mr Cosgrove held the Waimakariri seat from 1999 to 2011, but lost it after boundary changes affected the demographics of his electorate.

He has been a member of the Labour Party since age 14, and was later a protégé of former Prime Minister Mike Moore, running his campaigns in the 1990 and 1993 elections.

After entering Parliament, he held several ministerial portfolios including building and construction, associate finance, immigration, small business, responsibility for the Rugby World Cup, and associate justice.

He said his biggest achievements were reforms of the real estate and property sector, improving quality in the construction sector, and leading the development of the business case for the redevelopment of Eden Park for the 2011 Rugby World Cup.