The 32-year-old Frenchman arrived at Pride Park in January as a free agent, signing a deal until the end of the season with the Barclays Premier League basement club.
But the former Newcastle and Portsmouth player made only three starts for the Rams and headed over to Canada for a trial this week.
Derby manager Paul Jewell told his club's website, dcfc.co.uk: "It didn't quite work out for Laurent here, but we wish him well in the future."
"He's a tremendous player with a lot of talent, and we expect him to come in and make an impact with our club straightaway.
"He's played at every level and is a true professional in every aspect."
Robert's biggest career move came when he signed for Newcastle in 2001 and played under current Toronto coach John Carver.
"I've spent a lot of time with Laurent and know a lot about his game," said Carver.
"He'll be a big asset to the team."