Former deputy premier Nathalie Normandeau is testifying at the province's corruption inquiry.
Normandeau's name has been mentioned frequently during testimony at the Charbonneau Commission.
The former Liberal cabinet minister is the highest-ranking politician to take the stand at the probe.
Normandeau has been on the defensive over the past several months amid swirling allegations.
Anti-corruption police officials have alleged in warrant documents that she intervened in favour of the Roche engineering firm against the advice of civil servants.
However, no charges have been laid and the allegations have not been tested in court.