Whanganui MP and deputy speaker Chester Borrows will stand down at next year's election.
Mr Borrows - who is headed to trial over a charge of careless use of a motor vehicle causing injury - entered Parliament in 2005 and was a former Minister of Courts.
He said he had always thought that four terms would be an ideal tenure, and was particularly proud of the youth justice reforms he worked on.
"As far as work goes, I'd like to work in the justice space, or welfare or something like that. That's what pushes my buttons, and that's where I'd like to go."