TORONTO - Longtime Progressive Conservative and former Ontario cabinet minister Elizabeth Witmer is leaving politics after being re-elected just six months ago, opening the door to a potentially game-changing byelection.

Witmer is resigning as the member for Kitchener-Waterloo after 22 years in the legislature to take on the government-appointed post of chairwoman of the Workplace Safety and Insurance Board.

The move could give the minority Liberals a shot at tipping the scales in their favour.

The Liberals were re-elected last October just one seat short of a majority government. The election of Liberal Dave Levac as Speaker means they currently have 52 votes in the 107-seat legislature.

But if the Liberals manage to snag Witmer's riding from the Tories, that would put them on equal footing with both opposition parties, who collectively hold more seats. And the Speaker, who can only vote if there's a tie, traditionally sides with the government.

Shortly after Witmer announced her resignation, the government issued a release that Premier Dalton McGuinty had nominated her for the top post at WSIB, a government agency that provides workplace insurance.

"Elizabeth Witmer is exceptionally gifted to be the chair of the WSIB," McGuinty said in a statement Friday.

"Elizabeth will bring strong leadership to the WSIB board as they work to eliminate the unfunded liability while helping injured workers and reducing red tape for business."

The WSIB has been a frequent target of the Tories, who have complained that the premiums it collects from businesses are killing jobs and have criticized its connections to the Liberals, including departing chairman Steve Mahoney.

Witmer called her decision to leave extremely difficult, but said she felt it was the right move for her at this point in her life and career.

She dismissed suggestions, however, that her choice had anything to do with the direction the party was taking under current leader Tim Hudak.

"It had everything to do with me, my life and my career and what was right for me at this time," she said.

"I leave the party, and it's been made easier for me because I feel it is in very good hands; I believe that we are well positioned for the future."

She also shrugged off the implications of a byelection in her long-held riding because of her departure.

"I don't think there's ever a right or wrong time to leave," she said. "Events happen in your life and you make decisions."

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

"Elizabeth Witmer has served our province with grace, integrity and distinction and helped guide us through some very challenging times," he said in a statement.

"The Ontario PC Party will forever be grateful to Elizabeth Witmer for the leadership, dedication, guidance and service she has given our party. She will always be an elder stateswoman of the Ontario PC Party. We wish her well in her new endeavour."

NDP Leader Andrea Horwath issued a one-line statement on the departure, saying that while the two "rarely saw eye-to-eye," Witmer "has been a strong voice in the Ontario legislature and I’ll miss her as a colleague.”

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

She was first elected to the legislature in 1990 and served as deputy premier in the Tory governments of Mike Harris and Ernie Eves from 1995 to 2003.

She also took on several cabinet posts, including health and long-term care, education, labour and the environment, where she presided over the first closure of a coal-fired generating plant.

Witmer sought the party's leadership in 2002, but lost to Eves.

During the race, she vehemently opposed leadership rival Jim Flaherty's promise to make homelessness illegal and jail those who persisted in living on the streets.

"I find his plan absolutely disgusting," she said at the time. "It is inhumane and is totally lacking in compassion. He has no appreciation and he has no understanding of the root causes of homelessness."

Most recently, Witmer took up the fight to eliminate bullying in schools, tabling a bill which received second reading in the legislature with unanimous consent.

Also on HuffPost:

Loading Slideshow

• Recent Federal Floor Crossers

  <a href="http://www.huffingtonpost.ca/2012/01/10/lise-st-denis-ndp-join-liberals_n_1196406.html?ref=canada-politics">Lise St-Denis' defection from the NDP to the Liberals</a> has put crossing the floor back in the news. Here's a list of other recent federal floor crossers.

• Lise St-Denis

  The newly elected NDP MP jumped ship to the Liberals just 5 months after the federal election of 2011. St-Denis faced harsh criticism from those who saw the move as disregarding the will of her constituents. Many argued that voters in St-Denis' Quebec riding had voted for Jack Layton and not for her.

• Belinda Stronach

  In 2005, Belinda Stronach, Conservative MP and daughter of billionaire Frank Stronach, crossed the floor and joined Paul Martin's Liberal Party. She was named Minister of Human Resources and Skills Development and Minister responsible for Democratic Renewal.

• David Emerson

  In 2006, Liberal MP David Emerson joined the Conservatives just two weeks after being elected. He was named Minister of International Trade and Minister for the Pacific Gateway and the Vancouver-Whistler Olympics.

• Wajid Khan

  In 2007, Wajid Khan jumped from the Liberals to the Conservatives after then-Liberal leader Stéphane Dion stated that Khan would not be permitted to continue in his role as an advisor to Stephen Harper.

• Carolyn Parrish

  Carolyn Parish was suspended from the Liberal caucus in 2004 after stomping on a George Bush doll for a "This Hour Has 22 Minutes" sketch. The outspoken MP subsequently decided to sit as an independent.

• Keith Martin

  In 2004, Canadian Alliance MP Keith Martin renounced his party to sit as an independent and announced he would seek to run as a Liberal in the next election. His move was a response to the merger between the Canadian Alliance and the Progressive Conservatives. He would go on to win the Liberal nomination in his riding and the election and sat in the Liberal caucus until his retirement in 2011.

• Bob Rae

  While Bob Rae isn't technically a floor crosser (he didn't switch parties while sitting as an MP) the interim Liberal leader did switch parties. Rae governed Ontario has the province's NDP premier from 1990-1995. In 1996 he resigned as leader of the Ontario NDP and in 1998 resigned from the party altogether. He returned to politics in 2006, joining the Liberal Party and running for its leadership. He was defeated in his leadership bid by Stéphane Dion, but won the federal riding of Toronto Centre in 2007.

• Ujjal Dosanjh

  Ujjal Dosanjh shares a similar story to Bob Rae. He served as NDP premier of B.C. from 2000-2001, but later joined the federal Liberals. He served as an Liberal MP from 2004 until his defeat in the most recent federal election.