OTTAWA—A political firestorm surrounding Canadian Prime Minister Justin Trudeau became more damaging Wednesday, as his ex-justice minister accused his top aides of repeatedly pressuring her to drop the prosecution of a global engineering and construction firm.

The testimony delivered by Jody Wilson-Raybould to a parliamentary committee offered the most detailed version yet of events fueling a scandal that risks upending Mr. Trudeau’s re-election effort later this year. She said that between September and December, she and...