Olin was born to a Jewish family in Chicago, Illinois, the son of a former Peace Corps official and pharmaceutical company owner. He was raised in Highland Park, Illinois. He graduated from The Putney School in Putney, Vermont, in 1972. He then completed his college career at the University of Pennsylvania. He is married to his thirtysomething and Brothers & Sisters co-star, Patricia Wettig, with whom he has a son, Clifford, and a daughter, Roxanne, who appears on The City.

As an actor, Olin played Michael Steadman on Thirtysomething (1987–1991) and Dr. Roger Cattan on L.A. Doctors (1998–1999). He was also noted for his performance as Detective Harry Garibaldi on Hill Street Blues and as the lead character in the short-lived EZ Streets. Olin has also appeared in other series, including Falcon Crest (as Father Christopher Rossini), Alias (as David McNeil), Murder, She Wrote, and the television movies Flight 90: Disaster on the Potomac (1984) and A Stoning in Fulham County (1988). In 1995, Olin starred as Bradly Morris Cunningham in the made-for-TV film Dead by Sunset, which aired on the Lifetime television network. The film was based on the best selling true crime novel of the same name by Ann Rule. His film credits include roles in Ghost Story (1981), Queens Logic (1991), and 'Til There Was You (1997).

Prior to working on Brothers & Sisters, Olin produced and directed episodes of Alias. He has directed episodes of L.A. Doctors, The West Wing, Felicity, Judging Amy, Freaks and Geeks, thirtysomething, and EZ Streets. In 2012, Olin co-starred on the ABC drama pilot Americana. He appeared in the video "Burnin' for You" by Blue Öyster Cult, in 1981. He is currently the executive Producer of This Is Us on NBC.