Sylvie Robitaille, a spokeswoman for a Montreal hospital, says Marc Couture, a worker at the plant, died at the hospital Saturday evening.
She said Sunday that Couture suffered burns on 90 percent of his body and was in an induced coma.
The bodies of two other people were found in the ruins of the plant in Sherbrooke, Quebec, after the explosion on Thursday.
The blast could be heard for miles (kilometers) and 18 others were hospitalized. Robitaille says three people remain hospitalized with non-life-threatening injuries.
The plant belonging to Neptune Technologies & Bioressources produces and exports health products.