Urich was of Rusyn and Slovak extraction and raised Roman Catholic in the small town of Toronto, Ohio, where he is honored with the Robert Urich Interchange leading to State Route 7. Due to the similarity in names with Toronto, Ontario, many sources list him incorrectly as being a Canadian. His second wife, Heather, actually is a Canadian from the latter city. Urich attended Florida State University on a football scholarship. In 1968, he earned a bachelor's degree in Radio and Television Communications. While attending, he joined Lambda Chi Alpha Fraternity. He went on to Michigan State University after working in Ohio to earn a master's degree in Broadcast Research and Management.

Urich was first married to actress Barbara Rucker (1968–74). He married actress Heather Menzies in 1975, and they remained married until his death in 2002. Menzies had played one of the von Trapp children, "Louisa," in the film version of The Sound of Music. Urich and Menzies adopted three children, Ryan, Emily and Allison. Menzies also battled cancer, and is an ovarian cancer survivor. She works with the Robert and Heather Urich Fund for Sarcoma Research at the University of Michigan Comprehensive Cancer Center.

Between 1973 and just prior to his death in 2002, Urich had lead or supporting roles in no less than 19 television series and miniseries (including several documentary programs). He also regularly hosted National Geographic TV specials and the National Geographic Explorer documentary series. He was the guest host of Saturday Night Live in March 1982. He made a noteworthy screen appearance opposite Clint Eastwood in the 1973 Dirty Harry film Magnum Force playing a vigilante motorcycle-patrol police officer.

Urich was the spokesperson for Bayer Aspirin in 1990 and for Purina dog food in 2000. In 1992, Urich hosted the CBS TV special The Bat, the Cat, and the Penguin, which was a behind-the-scenes look of the upcoming motion picture Batman Returns. Most of his TV series were short-lived, although several, such as Vega$ and Spenser: For Hire, proved to be successes. In 1988 he made a cameo appearance as 'himself' in an episode of Cheers, which was Boston-based like his own series 'Spenser'. In the 1990s, Urich reprised the role of Spenser in several made-for-TV films. He also played a main character, "Jake Spoon," in the acclaimed television miniseries Lonesome Dove, a role for which he received many positive reviews, as well as the lead in a 1996 Hallmark Hall of Fame production of Captains Courageous. He hosted numerous 'made-for-TV' shorts with such titles as, "When Animals Attack...."

In 1996, Urich announced that he had been diagnosed with a rare form of cancer, synovial cell sarcoma, that attacks a person's joints. The TV series he was working on at the time, The Lazarus Man, was ultimately canceled, his failing health cited by him as the reason. He continued to appear in film and TV during treatment. Urich ultimately died from the disease on April 16, 2002 at the age of 55. His final TV series role was in the sitcom Emeril, in 2001.