Boisclair, whose two-year tenure as PQ leader ended in 2007 shortly after he led the party to one of its worst electoral performances, was appointed Quebec's delegate-general to New York in early November.
But what angered some politicians on Tuesday was confirmation that Boisclair has also been named assistant deputy minister in the International Relations Department.
That appointment, endorsed in a Nov. 28 cabinet decree, allows Boisclair to remain in the civil service on a permanent basis.
The 46-year-old will be guaranteed an annual salary of $170,000 and will then be able to start taking his full pension at the age of 55.
International Relations Minister Jean-Francois Lisee acknowledged it is the first time a Quebec government representative outside the province has double-dipped in such a way.
Marois said Boisclair is extremely competent and has overseen thousands of civil servants in his various cabinet portfolios.
"He almost became premier of Quebec, he could have been premier of Quebec," said Marois, who was defeated by Boisclair for the PQ leadership in 2005.
"He got more than one million votes in the 2007 election and then he completed his postgraduate studies in the United States. This is a man who has strong interpersonal skills and a lot of talent."
Boisclair's PQ finished a disappointing third in the that election behind the minority Liberals and the now-defunct Action democratique du Quebec.
Lisee said Boisclair's second appointment should have been made public at the same time as the New York job.
"I don't think there was any intent to camouflage it because it was going to come out at some point," Lisee said.
''But from a communications point of view, it would have been better to do it the same day.''
Boisclair sought permanent status in the civil service because his New York appointment meant he had to renounce his consultancy work, Lisee noted.
''He asked us if it was possible to have some security. And in this case, given the quality of his candidacy, we thought it was worth it.''
However, Quebec solidaire denounced the appointment, calling it favouritism.
''At a time when the Quebec government is asking the middle class and even poor people to tighten their belts, we are asking Mr. Boisclair to give up the dual functions,'' said Francoise David, one of the left-wing party's two members in the national assembly.
''Frankly, we find it indecent.''
Elected at age 23 in 1989, Boisclair admitted in 2005 to personally using cocaine while serving as a member of the legislature between 1996 and 2003.
He served as a cabinet minister between 1998 and 2003, holding the immigration, social solidarity and environment portfolios. He quit politics in 2004 to attend the John F. Kennedy School of Government at Harvard University before beoming PQ leader.
He has since worked in academia and was a consultant with a Calgary-based energy company when he was recruited by Marois' government. It was while he was with the Alberta company that he knocked the PQ's opposition to shale-gas development.
— With files by Alexandre Robillard in Quebec City