By a 5-4 margin, the top court decision released Friday says the province's civil code is constitutional in its treatment of the financial entitlement of couples who are not legally married and who separate.
The decision means Quebec remains the only province that does not recognize "de facto" marriages.
The ruling has broad implications in a province where the 31.5 per cent of couples report being in de facto relationships, versus an average of 12.1 per cent in the rest of Canada.
Justice Louis LeBel, writing for the five-judge majority, said there was no charter violation at play because the current provincial law promotes autonomy.
"The Quebec National Assembly has not favoured one form of union over another," he wrote.
"The legislature has merely defined the legal content of the different forms of conjugal relationships. It has made consent the key to changing the spouses' mutual patrimonial relationship.
"In this way, it has preserved the freedom of those who wish to organize their patrimonial relationships outside the mandatory statutory framework."
While the province's Civil Code does not regulate the status of de facto spouses, some laws — including those governing social assistance, income tax and Quebec's Pension Plan — treat them as a couple.
The case that sparked the debate, known as Lola vs. Eric, had been making its way through the court system for years. It involved a Quebec couple who never married, but lived together for seven years and share three children.
A court order prevents the publication of the parties' real names.
Pierre Bienvenu, the lawyer representing "Eric," said his client is relieved the long court process is over and is satisfied with the decision.
"It is really by force that he was dragged into this long debate," Bienvenu said.
After separating, Lola sought spousal support, but Quebec's Civil Code provides no such provision for couples who are not legally married.
Lola had been seeking a $50-million lump-sum payment as well as $56,000 a month from her former spouse — a well-known Quebec business tycoon known in the case as Eric. Lola was 17 when she met the then 32-year-old entrepreneur.
When they split, Eric agreed to pay generous child support — but he rejected the lump sum and annual alimony settlement claim.
The woman took her case to the Quebec Superior Court in 2009, when a judge rejected her claims, saying that under existing law, partners in a de facto relationship have no rights, duties and responsibilities to each other — no matter how many years they've lived together.
Lawyer says 'ball back in legislators' court'
In November 2010, a Quebec Court of Appeal decision invalidated that section of the civil code, saying the law discriminates against unmarried couples, and the province was given one year to change the law.
The Quebec government described that ruling as a mistake, and appealed to the Supreme Court.
Guy Pratte, the lawyer who argued Lola's case, said Friday morning that he was disappointed with the decision, but it doesn't mean the matter is settled.
"The implication for Quebec society is that the ball is now back in the legislators' court."
Quebec Justice Minister Bertrand St-Arnaud said the decision "confirms the principle of freedom of choice which has always governed life in Quebec, in other words the freedom of couples who choose the rules that will govern their union."
He said there are already a number of options open to unmarried couples who want the same rights as married couples, including civil unions and a cohabitation contract.
St-Arnaud also said it may be time for a "general reflection" on the status of families under the law.
"It's true that in the last decade, our social and family realities have evolved, and is it time for us to start to think again about the regime in our civil code? Maybe."
Statistics Canada says nearly 1.4 million Quebecers are in what the federal agency calls "common-law" relationships, according to the 2011 census, and about 60 per cent of children are born to such unmarried couples.