Sonia LeBel, a Crown prosecutor who had already been working with the Charbonneau Commission, has been named to the post.
LeBel replaces Sylvain Lussier, who resigned in mid-October after allegations of conflict of interest.
The veteran lawyer had, in the past, represented a construction firm that was named at the inquiry.
The high-profile corruption inquiry has already heard of bid-rigging, political corruption and Mafia ties in the construction industry as well as allegations of illegal party financing.
Lussier said in his resignation letter to the commission that while any conflict allegations are unfounded, he had decided to quit to ensure the integrity of the process.
LeBel, called to the Quebec Bar in 1991, has spent the last two decades as a Crown prosecutor.
She has vast experience in cases involving drugs and organized crime and has spent the past few years prosecuting murder cases in Montreal.