On a suggestion from playwright Theresa Rebeck, Criminal Intent executive producer René Balcer hired Leight to join the staff of the series in its second season as a writer/producer. His colleagues included a reference to Leight's play Side Man in a third season episode, "Shrink-Wrapped"; a bickering couple argues about the motivations of the married couple in the play. Upon a recommendation from Balcer, Leight was named the show's executive producer and head writer in 2006 when Balcer left the show at the end of the fifth season. In 2008 he left the show after the seventh season he was replaced with Walon Green, Robert Nathan, and Ed Zuckerman to be the new showrunners for the show starting with the eighth season.