Wayne Elhard represents Cypress Hills, one of the largest rural ridings in the province.
Premier Brad Wall says Elhard has been a leader in the party caucus and calls him irreplaceable.
Elhard was the first person elected under the party's banner in a 1999 byelection.
He was re-elected later that year in a general election and then again in 2003, 2007 and 2011.
Elhard says it's been a pleasure to serve on behalf of his constituents.
He says he will continue in his role until the next provincial election, expected in April 2016.