The 24-year-old also plotted to kill Canadian PM Justin Trudeau, prosecutors told a Canadian court.
Actor Ryan Grantham, pictured in 2013, appeared in the TV shows Riverdale, Supernatural and the 2010 film Diary of a Wimpy Kid
The 24-year-old, who played Jeffery Augustine in teen drama Riverdale, was sentenced at British Columbia Supreme Court in Vancouver on Wednesday. After drinking beer and smoking marijuana for hours following the murder, he packed a car with three guns, ammunition and 12 Molotov cocktails he had made, as well as camping supplies and directions to Mr Trudeau's Rideau Cottage residence.
The court also heard Grantham had considered committing an act of mass violence at Vancouver's Lions Gate Bridge or at Simon Fraser University, where he had been a student, en route before turning his car around and handing himself in.