Arkin guest-starred in the award-winning television show "Happy Days" in episode 35, season 2 in 1975. Also in 1975, he made a guest appearance on "Barney Miller" (episode: "Grand Hotel"). His first starring role in television was as Lenny Markowitz, the central character in the 1977 situation comedy "Busting Loose". He since has appeared in various television series such as "A Year in the Life" (1988), "The Twilight Zone" (1986), "Northern Exposure" (CBS, 1990–95), where he played the mercurial barefooted chef Adam, and "Chicago Hope" (CBS, 1994–2000). He appeared in two "Law & Order" episodes, "Self Defense" (season three, 1992) as jewelry store owner George Costas and "Red Ball" (season 16, 2005) as a district attorney named Charles Graham. He also appeared in "Picket Fences" (season two, episode 13). Other television appearances include "The West Wing" (1999) (as trauma specialist and psychiatrist Dr. Stanley Keyworth), "Frasier", as an obsessive fan of Frasier's, for which he was nominated for a Primetime Emmy Award for Outstanding Guest Actor in a Comedy Series, "Boston Legal", "Baby Bob", "Monk" and "8 Simple Rules for Dating My Teenage Daughter" (2002). In 2007, he starred in the NBC drama "Life" in the role of Ted Earley. He played a white separatist leader named Ethan Zobelle during the second season of the FX series "Sons of Anarchy" reuniting with former "8 Simple Rules" castmate Katey Sagal. In 2011, he appeared in "The Closer" episode "To Serve With Love" (season seven) as a suspect named Steven Hirschbaum. He also portrayed mob boss Theo Tonin on "Justified" in 2011, and an FBI agent in "The Chicago Code", also in 2011.