Voters in Vaughan and Kitchener-Waterloo will be going to the polls on the Thursday after Labour Day.
"Our message to voters will be clear. We need your vote to send Ontario Liberal MPPs to Queen's Park so we can push through opposition games and work to balance the budget and protect our world class public education system," McGuinty said Wednesday at a school in Maple, just north of Toronto.
McGuinty called the byelections on Wednesday to fill the two seats vacated by Liberal Greg Sorbara and Progressive Conservative Elizabeth Witmer.
Sorbara resigned last week to devote himself to running the Liberals' election campaign, while Witmer was given a plum appointment by McGuinty to head the Workplace Safety and Insurance Board.
Liberals need 2 byelection wins for majority
Sorbara's resignation leaves the Liberals with 52 seats, one less than the combined Progressive Conservatives and New Democrats. The Liberals need to win both byelections in order to secure the 54 seats required for a majority government.
McGuinty toured the school in Maple just before making the announcement, and says for him making sure there's labour peace in schools is the key issue in the byelections.
The premier also says calling the byelections does not mean he has ruled out calling the legislature back in an emergency session this month to impose a new contract on Ontario teachers.
McGuinty admits governments always have a difficult time winning byelections, but says the Liberals are the only party with a plan to secure a public sector wage freeze to eliminate the deficit.