McGuinty said at a Friday news conference that Ken Coran, president of the Ontario Secondary School Teachers' Federation, told him earlier Friday morning that his union is no longer asking its members to hold a one-day protest Wednesday.
The move to back off next week's walkout comes after a labour board ruled a similar walkout planned by elementary teachers for Friday would be illegal.
Sam Hammond, president of the Elementary Teachers' Federation of Ontario, ordered his members to comply with the ruling by the Ontario Labour Relations Board (OLRB) shortly after it was issued at 4 a.m. ET Friday.
"I want to thank the ETFO and OSSTF union leadership for acting responsibly in the face of the OLRB decision," McGuinty told reporters.
The OLRB decision came just a few hours before thousands of educators were due to stage a one-day walkout to protest the Liberals' decision to impose two-year contracts under Bill 115, a controversial anti-strike law.
The teachers' unions have argued that the legislation is unconstitutional and will fight it in court.
"This [OLRB] ruling now puts the remaining questions around Bill 115 squarely in a sphere of the courts," McGuinty said.
"The courts will rule on the constitutionality of our legislation. Teachers' unions can make their case in that forum, and so will we. And that’s exactly the way it should be."
Under Ontario's labour laws, engaging in illegal strike activity can carry a penalty of up to $2,000 per person and up to $25,000 for a trade union.
Confusion, frustration for parents
McGuinty's comments come on a confusing morning for parents, who had gone to bed thinking the elementary teachers' walkout would close schools today. They woke up to find out the protest was cancelled after the early-morning ruling.
Several school boards had already decided to close their elementary schools in anticipation of the protest but in the wake of the ruling, many boards, including all Toronto-area school boards, decided to open schools.
In the end, eight Ontario school boards opted not to hold classes on Friday, including boards in the Ottawa area and Windsor.
Many parents turned to Twitter to vent their frustration at not knowing whether to take their kids to school. Many reported dropping their children off to half-empty classrooms.
Rebecca Cameron told CBC News the uncertainty surrounding the dispute is confounding for parents.
"We didn't think we'd be here," she said while dropping off her kids at a Toronto school. "I'm frustrated. It would be nice to have everything constant and resolved, and know what to expect every day."
Other parents expressed support for the teachers, saying they back their right to collective bargaining.
McGuinty said he hopes that with Friday’s ruling in the books and a two-year contract in place, teachers and the province can “begin laying groundwork for more productive negotiations next time.”
While the dispute has waged, some teachers have stopped supervising sports teams, clubs and other extracurricular activities.
McGuinty said if teachers resume these duties, it would be “an encouraging step forward.”