Jean-Francois Lisée will be the third candidate to become the new leader of the Parti Quebecois.
The MNA for Rosemont will make his official announcement on Monday morning.
Last week Lisée told CTV Montreal that he would only run if he thought he could bring "something to the table that is not on offer among these other excellent candidates."
That "something" would be a promise that the Parti Quebecois, devoted to sovereignty, would not hold a referendum on independence in its first mandate.
"My answer is no, and you have to say no clearly. Not because we don't want independence, but we want it to succeed," said Lisée.
"I've been in this business for 30 years. There is no way that we can have a mandate in 2018, in 24 months. And we're not even ready."
In a blog post on Monday Lisée said the first priority for the PQ had to be eliminating the "quasi-monopoly" that the Liberal party has on power in Quebec, and that the PQ could work on sovereignty in the future.
"Nothing would be more gratifying that accomplishing those two tasks simultaneously, in two years, in the October 2018 election. But nothing would be worse than to be served another refusal by the Quebec people."
"We know the majority reject the idea of another referendum (or any step toward sovereignty). Trying to force through this blockade will push more electors into the arms of the Liberals and assure them another victory," wrote Lisée.
"The naked reality is that a significant portion of our fellow citizens, including francphones, are allergiec to not only the word referendum, but to any proposition that will direct them toward such a rendezvous."
He added he would like to hold a referendum on independence in 2022.
Lisée was intimately involved with the 1995 referendum, and served as then-Premier Jacques Parizeau's speechwriter at the time. He penned the speech that Parizeau recorded in the event of a 'Yes' vote in 1995.
Two other MNAs have already declared their intent to become leader, namely Veronique Hivon and Alexandre Cloutier, while Martine Ouellet is expected to officially declare her bid later this week.
Cloutier and Lisée both ran for the PQ leadership last year, although Lisée dropped out with a declaration that the PQ membership needed to have its "PKP moment", in recognition of the desire for the PQ rank and file to have the business leader as its chief.
Pierre Karl Peladeau resigned as the PQ leader and the MNA for St. Jerome earlier this month, less than one year after being chosen PQ leader, citing familial obligations.
