Ray Novak, Harper's chief of staff, began phoning ministers and cabinet newcomers with their new assignments on Saturday night, with the formal appointments set to be announced Monday morning at Rideau Hall.
It marked the end of a long process that began early this year, when Harper's office began telegraphing its plan for a significant mid-term shakeup in both the federal cabinet and in its policy direction.
The shuffle — expected by all accounts to be the biggest overhaul since Harper first took power in 2006 — means the arrival of a number of new faces, the departure of several familiar ones and a rousing game of musical chairs for the rest.
Calgary MP Michelle Rempel, parliamentary secretary to Environment Minister Peter Kent and a strong performer during question period, is among the new additions to cabinet, Conservative sources familiar with the changes told The Canadian Press.
Kent himself is leaving, as is junior transport minister Steven Fletcher, said the sources, speaking on condition of anonymity in advance of Monday's formal announcement. Five other ministers have already indicated their departure plans.
Public Works Minister Rona Ambrose, Heritage Minister James Moore, Human Resources Minister Diane Finley and junior minister Maxime Bernier are all moving to new portfolios, sources say.
Behind the scenes, many Conservatives have identified the need for generational change in order to go up against 41-year-old Justin Trudeau's reinvigorated Liberals and Tom Mulcair’s NDP, a party already chock-a-block with young MPs and high-profile women.
"It's going to be a substantial shuffle," said one senior Conservative. "New faces, younger members, along with experienced hands. New women in cabinet."
There has been corridor talk of a "constructionist" shuffle in the works. Harper leans heavily on his cabinet committees, which is where the real decisions are made, and any change to committee structure or personnel could prove significant.
The cabinet shuffle is seen as one step in a three-stage effort to shake the governing Conservatives out of a mid-mandate malaise. A throne speech setting out refreshed policy themes is widely anticipated this fall, followed by a Conservative party policy convention in Calgary at the end of October.
A cabinet makeover has long been in Harper's plan but with the Conservatives routinely polling behind Trudeau's Liberals this spring and the toll taken by the Senate spending scandal, the shuffle has taken on a new urgency.
It was supposed to take place earlier this month, but was delayed by the rail disaster in Lac-Megantic, Que. Harper met with some ministers after Canada Day at his summer home at Lake Harrington northwest of Ottawa, getting their read on how they did in their portfolios, and giving them hints on where he saw them going next.
"You're going to be seeing the teams and the people that are really fighting it out for power in 2015," said Jason Lietaer, a principal at government relations firm ENsight Canada and a former Conservative insider.
"The prime minister is setting his lineup for the upcoming battle."
Lietaer is among those who believe Harper will continue to play his winning hand from the 2011 election that finally delivered the Conservatives their long-sought majority — economic competence and stability.
That means several key government stalwarts will be staying put, while lesser cabinet portfolios are shuffled around them.
The Conservatives have spent at least $113 million of taxpayer funds since 2009 on feel-good "economic action plan" advertising, and the government believes that branding is its trump card.
"The economy will continue to be our priority," the senior Conservative said.
Some well-connected Conservatives argue that if Finance Minister Jim Flaherty and Foreign Affairs Minister John Baird don't move, the cabinet makeover falls short of being a fundamental reset.
All eyes will be on Flaherty, and all indications appear to be that Harper will stay the course with the only finance minister he's ever appointed.
A recent exodus of staff from Flaherty's office had fuelled speculation he could be on the way out, but the former Ontario finance minister has openly lobbied to keep his job and says he wants to stay on until the government's top priority — a balanced federal budget — is achieved, likely in 2015.
Flaherty is battling a painful skin disorder and many expect he won't run again federally. Harper told cabinet members this winter to tell him if they were bowing out in 2015, as he would want to replace them this summer.
To be sure, the prime minister has some gaps to fill.
Vic Toews announced his retirement from politics last week, opening up the important public safety portfolio and a spot for a Manitoba MP. With Fletcher also believed to be on the way out, that could pave the way for both Shelley Glover and Candice Bergen to enter cabinet.
Peter Penashue, Harper's former intergovernmental affairs minister, resigned over campaign spending irregularities and was defeated in a byelection in March.
Keith Ashfield has left his post as fisheries minister due to ill health.
Harper's popular junior finance minister, Ted Menzies, is also stepping aside, as is fellow Calgarian Diane Ablonczy.
Sen. Marjory LeBreton, the Conservative government leader in the Senate and cabinet member, is resigning her post.
Lietaer suggested that in areas where the government hasn't been able to get matters "over the finish line" — long-delayed environmental regulations on the oil and gas sector come to mind — "a fresh set of eyes" might help.
Top priorities over the next two years include pulling the trigger on a trade deal, getting approval for a pipeline from Alberta's oilsands to the tide line, and negotiating the proposed new federal job training grant with reluctant provincial governments.
Also on HuffPost