Stefanson was first elected as a legislature member in 2000 and became leader of the Progressive Conservatives and Manitoba's first female premier in 2021.
"Serving as (legislature member), minister and the first woman premier has been the honour of a lifetime," Stefanson, 53, said in the chamber Thursday.
"These roles allowed me to serve Manitobans and help pave the way for future generations of women in public service."
Stefanson was chosen by her fellow Tories to replace former premier Brian Pallister. The party was low in opinion polls and did not rebound before last year’s election, which saw the NDP sweep to power.
On election night, Stefanson said she would quit as party leader and did so three months ago.
Stefanson said she will vacate her legislature seat before the spring sitting resumes May 6. That will require a byelection in her Tuxedo constituency in Winnipeg.
The seat is historically a Tory stronghold, but the NDP finished a close second there in the last election.