Independent MP David Kilgour will vote in favour of the federal budget but against an NDP amendment, a move that backs opposition efforts to topple the government and leaves the fate of Parliament effectively in the hands of a single member.
Mr. Kilgour has said he was undecided on which way he would vote, but in recent days expressed concern about the direction of the minority Liberal government and the decision to give rookie MP Belinda Stronach a cabinet posting upon her defection from the Conservatives.
Thursday afternoon, however, Mr. Kilgour decided to follow the lead of the Conservatives and give only his support to the broader budget, but not the amendment struck as part of a Liberal deal with the NDP.
"The deciding factor in my decision is a concern about what the postponement of an election will do to Canada's fiscal position," he said in a statement posted on his web site.
"How many more hastily-made long term commitments will the government make if given the opportunity?"
The Liberals and NDP combined have 151 seats versus the 152 for the Conservatives and Bloc, who are aiming to bring down the government.
With independent MP Carolyn Parish siding with the Liberals and Mr. Kilgour with the Opposition, the vote now comes down to Chuck Cadman, who has broadly hinted that he would vote with the Liberals.
If that happens, the two sides would end in a tie (153 to 153) and Liberal House Speaker Liberal Peter Milliken would enter the fray, casting his tie breaking vote with the government.
The vote is scheduled to begin at 5:45 p.m. EDT.
Mr. Kilgour's announcement came during a day of dramatic turns, which have suddenly become the hallmark of the federal political scene. Within weeks, headlines coming out of Parliament have run the gamut from health scares and political defections to broken hears.
Early Thursday, a call by Independent MP Carolyn Parrish - whose support is crucial to the survival of the minority Liberal government - to CTV's Canada AM raised questions about her ability to make it to the House of Commons because of a sudden illness.
A spokesman later insisted that she intended to vote in the House, even if she had to get there on her hands and knees.
"You can quote me on this, she's going to make the vote if she has to crawl," spokesman Brian MacDonald told globeandmail.com, adding that she is in "a hell of a lot of pain" as result of either a ovarian cyst or kidney stones.
Ms. Parrish herself later said: "Come hell or high water, there's no frigging way I'm going to let one ovary bring the government down."
Thursday's Parrish scare is just the latest in a whiplash string of events that have besieged the nation's Capital.
At issue is the survival of Prime Minister Paul Martin's minority Liberals in a budget vote that mirros the vote faced by Joe Clark's government in 1979.
Mr. Clark's government lost the vote after the Liberal Whip, determined to beat the Tories, brought in a New Brunswick MP - fresh from back surgery - by ambulance for the ballot.
In a further echo back to that era, sources said Mr. Martin's Liberals sent a doctor to Ms. Parrish's Ottawa home Thursday to make sure she was fine.
If Mr. Martin's Liberals - who have the backing of the NDP on Thursday's vote - lose, the Prime Minister has vowed to dissolve Parliament and call an election. That would come nearly a year to the day that Canadians last learned that they would be sent to the polls.
Exiting Thursday's cabinet meeting, Mr. Martin admitted that government ministers talked "more than a bit" about the vote, but also indicated that their discussions went beyond that to also cover further government business on issues like trade disputes.
If the Liberals win the vote, he added, he expects Parliament to continue with business as usual.
"We have heard the conservatives say that if the government wins the vote tonight, things should return to normal, and I think that that is really what Canadians want," he said.
Early on in the day, all sides were getting their ducks in a row.
"It is our intention to have everybody in the house," a spokeswoman for the Conservatives said Thursday.
Liberal Whip Karen Redman also said that party expected to turn out in full force.
She said ailing Energy Minister John Efford, whose attendance had been in question, is in Ottawa and will be in the House for the vote. However, she said, the Liberals would honour the agreement to "pair" off to cover the absence of Conservative Darrel Stinson, who is undergoing medical treatment.
"I think it will be [Ontario Liberal MP]Peter Adams, who is not seeking re-election," she said in an interview.
"Peter has agreed to sit out if we need him to."
As for the likelihood of any further surprises before MPs make it inside the House for the vote, Ms. Redman would only say: "Oh gosh, because we're not aware of them that's what makes them surprises, so who knows."
Canadians were thunderstruck earlier this week when Ms. Stronach - often cited as the face of the moderate Conservative movement in Canada - held a press conference alongside Mr. Martin to announce that she was crossing the floor and would serve as Liberal Human Resources Minister.
The move sparked outrage among her former Conservative colleagues and some of the responses from across the country drew charges of sexism because of their personal nature. Ms. Stronach's decision also triggered sudden, intense interest in her personal life because of her relationship with Deputy Conservative Leader Peter MacKay.
Mr. MacKay retreated to his family's farm in Nova Scotia, admitting to reporters that the week's events had left his heart a little "banged up." He later returned to Ottawa to sit with his party for Thursday's vote.
Within a day of Ms. Stronach's move, the Liberal party faced its own short-lived crisis when MP Jim Karygiannis was rushed to hospital from the House of Commons complaining of chest pains.
He later received a bill of clean health and is expected to be in the House for Thursday's vote.