Former finance minister Greg Sorbara is quitting as a member of the Ontario legislature, but will stay on as chair of the Liberals' election campaign.

Ontario Premier Dalton McGuinty made the official announcement at Queen's Park on Wednesday morning.

Sorbara said he was leaving so he could devote more attention to preparing the Liberal Party for an election that could come at any time.

"Over the next many months I need to ensure that our party has the policy proposals, the political organization, and the financial resources to contest and win the next election," he told reporters.

He also said he would like to spend more time with his family and on his family business.

Sorbara quit the cabinet a few years ago but remained an influential adviser to McGuinty and co-chaired the Liberals' re-election campaigns.

Following his remarks at Queen’s Park, Sorbara tweeted that he was "looking forward to continuing in my roles as Campaign Chair and Chair of the Ontario Liberal Fund to pave the road to victory!"

Byelections coming 'sooner rather than later'

The resignation of the veteran Liberal from his Vaughan riding means McGuinty now has to call two byelections.

The premier must also call a vote in Kitchener-Waterloo to replace Conservative Elizabeth Witmer, who he appointed chair of the Workplace Safety and Insurance Board.

Sorbara's resignation leaves the Liberals with 52 seats, one less than the combined Progressive Conservatives and New Democrats.

McGuinty said both byelections will be held on the same date, but that date hasn't been decided yet.

However, the premier said that "we are in a sooner rather than later mode."

Sorbara predicted that the Liberals would be competitive in the forthcoming byelections.

"I think we’re going to have a strong candidate in Vaughan and we’re going to keep that seat and I’m determined to make that happen," he said.

"And I think the same thing about Kitchener-Waterloo."

Opposition reacts to resignation

The Tories praised Sorbara's public service, but said he was part of a Liberal government that racked up a record deficit and nearly doubled Ontario's debt in nine years.

"The fact is this province is in a mess; we have a jobs crisis and a fiscal crisis," said Conservative Rob Leone.

"I think the people of Vaughan and the people of KW need to hear that message."

The New Democrats stayed on the high road, thanking Sorbara for his years of public service and holding any criticisms for another day.

"While we may not always have seen eye to eye on the floor of the legislature, I appreciate Mr. Sorbara's determination and skill," said NDP Leader Andrea Horwath.

Some of Sorbara’s colleagues in the Liberal caucus also offered kind words about his record in public service.

"My wonderful colleague Greg Sorbara has helped improve the lives of so many over so many years," Energy Minister Chris Bentley wrote on Twitter. "Thank you Greg."

Richmond Hill MPP Reza Moridi tweeted that Sorbara’s "passion, determination & friendship are inspiring."

With files from CBC News