Henri-Francois Gautrin said the sovereigntist party could even form a majority government.
Gautrin, a member of the legislature since 1989, warned that the Philippe Couillard-led Liberals could be confined to the Opposition backbenches for a few more years yet.
Recent polls have suggested the PQ had a significant lead among French-speaking voters, who decide the majority of the province's 125 ridings.
That has fuelled speculation Premier Pauline Marois will call the election in early March, thus sending Quebecers to the polls in April.
Gautrin based his scenario on the Coalition for Quebec's Future losing support and having it gobbled up mainly by the PQ.
Marois could emerge with a slight majority or form another minority government with more seats, he told The Canadian Press.
Current standings in the national assembly are: PQ, 54; Liberals, 49; Coalition, 18; Quebec solidaire two; and two Independents.