Thor appeared in the 1991 films Hook and Curly Sue. He is best known for playing Lewis Dodgson in the 1993 film Jurassic Park. Thor had originally auditioned for the role of Ian Malcolm. While his character was a major part of the sequel novel, The Lost World, the character was left out of the film adaptation. He then worked as an acting coach in Los Angeles. He and his wife Alice Carter co-own Carter Thor Studio.

On June 4, 2014, he was charged with the sexual assault of a 13-year-old girl by the Los Angeles County Sheriff's office. He was released on $2.6 million bail, later reduced to $1 million. The Los Angeles District Attorney's office filed 14 counts against Thor, including kidnapping and sexual assault against a minor, specifically a 13-year-old girl who sought acting lessons. The District Attorney alleges that Thor gave the girl "a controlled substance ... marijuana" and sexually assaulted her. Thor pleaded not guilty to all 14 counts.

The alleged victim, Jordyn Ladell, named herself in an interview with The Hollywood Reporter shortly before the start of Thor's trial. Thor's trial began on August 17, 2015. At that time, 13 of the charges against him had been dropped in recent weeks. The only remaining charge was performing a lewd act on a child. The jury began deliberations after the trial ended on August 25. The next day, he was found guilty. In October, Thor's sentencing was postponed until November 20. That same month, Thor hired defense attorney Mark Geragos, to replace his previous Lawyer. On November 20, Thor's sentencing was postponed again until January 8, 2016. On January 8, Thor's sentencing was delayed until February 29, after Geragos filed a motion for a new trial based on insufficient evidence and "ineffective assistance of counsel". In March 2016, the judge denied Geragos' requests and reaffirmed the guilty verdict. On April 27, 2016, Thor was sentenced to six years in state prison.