Word of McGuinty's resignation leaked Tuesday night, upstaging Wynne's first big accomplishment as premier — passage of the minority government's budget.
The former premier issued a statement Wednesday saying he was resigning his Ottawa seat after nearly 23 years.
"The end of this session marks an opportune time for me to bring to a close my service to the people of Ottawa South," McGuinty said.
"I am proud to have been Ontario's first premier from Ottawa, and proud to have drawn my life's lessons and values from my parents' home in Alta Vista."
Wynne lauded McGuinty for serving the public with "vision and determination" and talked about his many accomplishments.
"He reminded us that government could build us up through investments in education, health care, research and innovation," she said in a statement.
"He steered this province through a global recession and three general elections."
Asked about McGuinty's legacy, Progressive Conservative Leader Tim Hudak said it was one of debt, waste and corruption.
"If you like what Dalton McGuinty has done to the province, you're in for even more of it under Kathleen Wynne," Hudak said.
The New Democrats said McGuinty's legacy was one of broken promises, from the implementation of the health care tax in his first year up to his resignation as an MPP when he promised to stay until the next general election.
McGuinty "did more harm than good," said NDP critic Peter Tabuns.
The NDP questioned the timing of McGuinty's announcement, just days after the provincial police launched a criminal probe into the destruction of emails about the cancellation of two gas plants by senior Liberal staff.
"The last time things got really hot on the gas plant file, he prorogued parliament and said he was not going to be premier any longer," said Tabuns.
"The events of the last few days have ratched that up substantially, and he takes the next step and resigns his seat."
Both opposition parties accuse the Liberals of deleting the email accounts to cover up the cost of cancelling gas plants in Oakville and Mississauga, which has ballooned to $585 million.
In a statement issued last Friday McGuinty denied he had ordered his staff to destroy government records on the gas plants in violation of the law.
The Tories and NDP want McGuinty to appear again at justice committee hearings into the gas plants to answer questions under oath about the mass deletions of emails.
McGuinty's two-page resignation statement makes no mention of his controversial decisions to cancel the two gas plants — a move the opposition says was aimed at saving Liberal seats in the 2011 election, when his party was reduced to a minority government.
"I leave politics with my idealism intact and a deep sense of gratitude for the opportunity to have served in public life," wrote McGuinty.
"It has been my greatest honour and privilege to follow in my father's footsteps."
Dalton McGuinty Sr. represented Ottawa-South until his death in 1990, when his son successfully ran to replace him.
The Liberals have scheduled a nomination meeting for June 20 in Ottawa South to pick a candidate to replace McGuinty in a byelection.
Wynne has six months to call the vote, but is expected to call it later this summer because she faces an Aug. 15 deadline to call byelections in Windsor and London to replace former finance minister Dwight Duncan and former energy minister Chris Bentley. Both men quit after Wynne was sworn in as premier in February.
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