The Liberal leader, who was fighting his first campaign as his party's chief, made it clear he would confront the Parti Quebecois' independence agenda head on.
He was accused of fearmongering by his opponents but his strategy paid off with a majority Liberal government on Monday night and the worst electoral defeat ever for the PQ.
Couillard, a popular health minister in Jean Charest's government until 2008, presented himself as a uniter when he addressed ecstatic Liberal supporters late Monday evening.
"We are all Quebecers," he said in his victory speech in his Roberval riding, which he captured from the PQ. "We should all focus on what brings us together.
"Let us say together, with passion, we're all proud of being Quebecers. My friends, division is over. Reconciliation begins."
Couillard said he accepted the victory with "serenity and humility" and promised to govern with integrity and transparency.
While Couillard's campaign was built on stoking fears of a sovereignty referendum, his election to the province's top job raises the question of whether he will follow through on a clearly stated interest in being the Quebec premier who signs the 1982 Constitution.
He raised the issue early in the campaign but quickly downplayed it when questions arose about how he would accomplish this and what demands he would make.
Couillard then treated it as an almost incidental matter, saying creating jobs would be his priority.
Previous Quebec premiers have ducked the Constitution issue, especially since the failures of the Meech Lake constitutional accord in the 1980s and the Charlottetown agreement a few years later rekindled sovereigntist fervour to bring the Yes side within a whisker of winning the 1995 referendum.
No federal leaders have shown any enthusiasm in engaging Couillard on the Constitution.
The PQ likely won't be pressing him on his plans for it either as it grapples with an eventual leadership race.
Marois announced Monday she would quit as PQ chief after losing not only the premier's job but also her own riding.
"Quebecers have spoken and we must respect their decision," a philosophical-sounding Marois said to disappointed supporters at a Montreal hotel.
She urged her troops to fight on and said she was proud of the accomplishments of her 18-month-old government.
Marois also expressed fears for the future of French in Quebec. Couillard has endorsed bilingualism although he has said language laws must be strictly enforced.
The Liberals ended up winning 70 of the 125 seats up for grabs, compared with 30 for the PQ and 22 for the third-placed Coalition for Quebec's Future. The leftist Quebec solidaire picked up one seat to bring its total to three.
In comparison, the PQ had 54 seats at dissolution.
In terms of popular support, the Liberals pulled in more than 41 per cent on Monday, a dramatic climb from 31 per cent in 2012. And the PQ finished the night at 25 per cent, just two percentage points more than the Coalition.
Couillard's victory came 18 months after voters, weary of nine years of Liberal rule under Charest and allegations of corruption within his party, turfed the Liberals out in favour of a minority PQ government under Marois.
Marois called the election on March 5 with the intention of riding a wave among some Quebecers for a secular charter that would have prohibited public-sector workers from wearing hijabs and kippas on the job.
The party figured the fertile ground of identity politics as well as tougher language laws would drive it to victory.
But then came media mogul and star PQ candidate Pierre Karl Peladeau announcing he was leaving the business world for politics to build an independent Quebec.
He delivered his message with a fist pump that might as well have been a punch to the PQ gut.
Peladeau's enthusiasm carried over to Marois, who mused for days about what a sovereign Quebec would be like, a contrast to other PQ leaders who downplayed sovereignty because of voters' distaste for referendums.
Although she quickly tried to move the discussion off sovereignty, Couillard hung on to it like a hungry dog with a meaty bone.
Two-thirds of Quebecers have said they don't want a third referendum on sovereignty. The other two were held in 1980 and 1995.
Support for the option hovers between 35 and 40 per cent in opinion polls and analysts have pointed out those who do back it are aging boomers.
Marois's defeat follows the crushing of the Bloc Quebecois in the 2011 federal election when it was reduced to four seats and is stunningly similar to one that brought her to the PQ's top job after Andre Boisclair suffered an electoral thrashing in 2007.
Boisclair won only 36 ridings that year.
The PQ nearly collapsed after that election, with Marois going on to win the leadership by acclamation. Monday's devastating blow to sovereignty will likely throw the party into upheaval again as it ponders its next move.
The red Liberal tide flowed early across Quebec's electoral map on Monday, sweeping through all regions over the incumbent PQ, which had been battered by questions about its plans for a third sovereignty referendum that most Quebecers flatly said they didn't want.
Coalition Leader Francois Legault, who had seen support for his party rebound in recent days, watched dejectedly as results came in, one hand gripping the side of a white couch as his wife sympathetically patted his knee. He later accepted the voters' decision with grace.
While no pundit would be foolish enough to declare sovereignty dead, the option has likely been put to sleep for a while. Some observers have suggested it could be years, if not decades, before it is revived.
Peladeau, on the other hand, won his Saint-Jerome riding on Monday and will likely be considered a possibe replacement for Marois.
Mnday's results in Quebec no doubt prompted a sigh of relief in Ottawa as well.
With the PQ out, it means Prime Minister Stephen Harper won't have to worry about a national unity crisis as he heads toward the 2015 election.
""On behalf of our government, I would like to convey my sincerest congratulations to Philippe Couillard on his election victory," Harper said in a statement.
"The results clearly demonstrate that Quebecers have rejected the idea of a referendum and want a government that will be focused on the economy and job creation. We look forward to working with the new government of Quebec on those priorities."
Ontario Premier Kathleen Wynnealso congratulated Couillard on his victory.
"I believe we can achieve so much when provinces and territories work together," she said in a statement.
"Ontario and Quebec have a long history of collaboration and productive relations, and we look forward to continuing our fruitful partnership by focusing on the things that matter most to people: good schools, reliable health care, a safe and clean environment and a strong economy."
British Columbia Premier Christy Clark also offered her congratulations.
"Like most Canadians, I have been paying close attention to the
provincial election in Quebec," she said.
"The Canada I have lived and worked in, the country that I am
humbled to represent around the world, includes Quebec.
"I look forward to working with premier-elect Couillard at the
premiers' table on our shared goals: building a proud, prosperous
and inclusive Canada."
The 33-day campaign had been considered as one of the nastiest in decades.
Voters had complained in the weeks leading up to the vote that bread-and-butter issues had received little attention as politicians fired potshots over the possibility of another sovereignty referendum or challenged each other on ethics.
Marois, whose party formed a minority government in 2012, was hoping to win a majority of the 125 ridings — a scenario that could have eventually led to another referendum.
"It is a beautiful day," she told reporters after she cast her ballot in the riding of Charlevoix-Cote-de-Beaupre, northeast of Quebec City.
"I am very serene at this moment. I trust Quebecers will choose a good government to lead them and I am confident about tonight."
Hours later, she would find out that the confidence was misplaced.
Recent opinion polls had indicated the momentum was with Couillard's Liberals, although analysts were leery about predicting the size of the win given polling blunders in the Alberta and British Columbia provincial elections and in the estimations of Quebec Liberal strength in 2012.
At dissolution, the PQ had 54 seats, while the Liberals had 49. The Coalition had 18, Quebec solidaire two and there were two Independents.
Voter turnout was 71.5 per cent, compared with 74.6 per cent in 2012.