Marc Couture, a worker at the plant, died at Montreal hospital on Saturday evening.
Sylvie Robitaille, a spokeswoman for the hospital, says Couture suffered burns on 90 per cent of his body and was in an induced coma.
The bodies of two other people were found in the ruins of the plant.
Robitaille says three people are still in hospital with non life-threatening injuries and that 18 people were injured in total.
The explosion was at a production plant belonging to Neptune Technologies & Bioressources, in Sherbrooke, Que.
The company produces health products, such as Omega-3, derived from marine life.