Redford's chief-of-staff, Stephen Carter, confirmed on Twitter on Friday that the three-term Vermilion-Lloydminster Progressive Conservative legislature member had resigned.
Snelgrove — finance minister and Treasury Board president under former premier Ed Stelmach — could not be reached for comment.
Danielle Smith, leader of the Wildrose party, said Snelgrove told her two days ago that he planned to sit as an Independent when the house resumes next month.
"I applaud him for standing up," Smith said in an interview. "It takes a lot of courage to go against a 40-year government.
"I think we're going to hear an awful lot over the coming weeks and months about how badly the Redford PCs are off track."
Smith said she had a two-hour conversation with Snelgrove about his concerns, which include the current government cabinet tour and how Redford overturned $107 million in education cuts last fall.
"He's very concerned about the direction that the government is taking — as are we — and I look forward to working with him in the legislature to hold the government to account," said Smith.
The spring sitting of the legislature begins Feb. 7, with a budget delivered by Finance Minister Ron Liepert scheduled for Feb. 9.
Snelgrove's relationship to the Progressive Conservative caucus became strained when Redford won the party leadership last fall and dumped him from cabinet.
Earlier this week, Snelgrove told the Lloydminster Meridian Booster newspaper that the current provincewide cabinet tour undertaken by Redford and colleagues is a cynical pre-election photo-op paid for by taxpayers.
"What we heard from Premier Redford was that she spent all summer (on the party leadership race) finding out, and knew everything that Albertans want to know, and she was prepared to start making changes," he told the newspaper.
"So to go out on a tour now and pretend it's anything more than a photo-op for the pre-election is a bit of a surprise.
"You have to listen to people all the time. Not just when it suits your schedule."
Snelgrove, 55, is not running in the next election, which by law must come this spring. Redford has not given an exact date when she'll drop the writ, but she's said it will come after the province passes the budget. That would put a vote sometime in April.
Snelgrove supported Redford's rival, Gary Mar, in the party race last year to replace outgoing premier Ed Stelmach.
Stelmach named Snelgrove president of the Treasury Board in 2006, which made him one of the two key money ministers.
Early last year, he was named finance minister when Ted Morton resigned to run in the leadership race.
Snelgrove's relationship with Redford was doomed before she even picked her cabinet in October. Snelgrove told the Meridian Booster after her victory that he didn't expect to serve in cabinet and would refuse a post if offered.
He also questioned the validity of Redford's narrow win over Mar.
"It's a little troubling that virtually one per cent of the population is all that picked the premier," he told the newspaper at the time.
The married father of four was first elected in 2001. Before that, he was a town councillor in Vermilion, east of Edmonton near the Saskatchewan boundary.
The move leaves the Tories with 67 members in the 83-seat legislature.
The Opposition Liberals have eight seats, the Wildrose party four and the NDP two. Dave Taylor is the lone member for the Alberta Party.
Richard Starke, a veterinarian and former Lloydminster city councillor, is running in the riding for the Tories in Snelgrove's place.
Snelgrove is the fifth Tory politician to cross the floor since the last election in 2008. Rob Anderson and Heather Forsyth joined the Wildrose in 2010. They said they couldn't stomach the top-down decision-making process under Stelmach.
They were joined later that year by Guy Boutilier, who had been expelled from caucus for questioning delays on construction of a long-term care facility in his Fort McMurray riding.
Raj Sherman was also booted from caucus in 2010 for criticizing government health policy. He joined the Liberals and last fall was elected party leader.
Under Redford, the Tories did get one back. Last fall, Liberal Bridget Pastoor joined the PC ranks. She said her move wasn't just about politics, but also about the chance to work with Redford.