Ontario Premier Dalton McGuinty’s Liberals will get a chance to regain the majority they lost in last fall’s election with the resignation of Tory MPP Elizabeth Witmer on Friday.

Her stepping down triggers a byelection, which may help tip the scales in favour of the Liberals which are currently one seat shy of a majority.

Witmer, who has served as Kitchener-Waterloo’s MPP since 1990, was nominated by McGuinty to take over as chair of the Workplace Safety and Insurance Board.

"This has been an extremely difficult decision to make but I believe it is the right decision for me at this juncture in my life and career," Witmer in a statement.

Witmer served as deputy premier in the previous Tory government and as a cabinet minister held the education, health and environment portfolios.

Last fall’s provincial election left the Liberals with 53 seats, the Progressive Conservatives with 37 and the NDP, 17. Speaker Dave Levac came from the Liberal ranks, meaning that prior to Witmer’s departure, the NDP and Conservatives could combine to defeat the government on a confidence motion.

With Witmer’s seat now up for grabs in a byelection that must be called within six months, a Liberal win would give the Liberals 53 seats (not counting the speaker) and the opposition parties with a combined 53 seats. Because the speaker votes with the government in the event of a tie, a Liberal win in Kitchener-Waterloo would give McGuinty a de facto majority.

In last October's vote, Witmer had 21,356 votes while Liberal candidate Eric Davis finished second with 17,837 votes.

Opposition Leader Tim Hudak, who served a Witmer's parliamentary assistant when she was health minister, said her advice and mentorship were "invaluable" and "will never be forgotten."

Considered one of the more moderate Tories and well-respected by all parties, Witmer is also the longest serving woman MPP in Ontario's history.