Jenkins worked as an actor with Trinity Repertory Theater Company in Providence, Rhode Island before breaking into film with a bit part in Feasting with Panthers (1974), a television movie.
Jenkins is probably best known for his recurring guest star role on HBO's Six Feet Under. He played Nathaniel Fisher, the deceased patriarch of the Fisher family who regularly appears to his family as a ghost, and in dreams. Jenkins played the role since the show began in 2001, through to its final season in 2005.
He acquired good critical notices as the blue collar mine worker dad that stands up for his daughter (Charlize Theron) in North Country.