Veteran NSW Nationals MP Duncan Gay has announced his retirement from politics after a 29-year career.

Mr Gay, 67, flagged his intention to retire after he lost the roads portfolio in January in Premier Gladys Berejiklian's cabinet reshuffle.

"As a young grazier from Crookwell, I would have never dreamed of being one of the state's longest serving ministers for roads", he said in a statement on Thursday.

"I could not be prouder of what we achieved in my portfolio over six years."

Ms Berejiklian said she enjoyed an "extremely strong and close working relationship" with Mr Gay during her time as transport minister and treasurer.

"He was valued for his wisdom and judgment and his experience will be difficult to replace," she said in a statement.

The former roads minister is best known for backing major infrastructure projects such as Sydney's $16.8 billion WestConnex toll road and the NorthConnex tunnel linking the M1 and M2.

However he has copped his share of criticism over WestConnex - a controversial project in Sydney's inner west - and stiff fines for cyclists.

Mr Gay was also known for his colourful use of language once accusing the inner city "chattering classes" of producing more air pollution over Sydney than heavy vehicles.

Outlining his achievements on Thursday, Mr Gay said he championed the movement of freight from "paddock to port".

"Under previous governments, freight was a dirty word," he said.

"I also proved the naysayers wrong and delivered flashing lights at every school in NSW and convinced people it was fashionable to wear a life jacket when boating."

Mr Gay was first elected to the NSW Legislative Council in 1988 and has been a member of the Nationals since 1974.

His last sitting day in the Legislative Council will be on June 22, two days after the NSW budget is delivered.