Kercheval trained under Sanford Meisner at The Neighborhood Playhouse in New York City. Kercheval made his Broadway debut in the 1962 play Something About a Soldier. He appeared off-Broadway in the 1972 Kurt Weill revue Berlin to Broadway with Kurt Weill, and can be heard on the cast recording. Additional theatre credits include The Apple Tree, Cabaret (replacing Bert Convy as Cliff), and Here's Where I Belong. In 1966, he appeared as the title character in the original Broadway production of Fiddler on the Roof, co-starring with Herschel Bernardi, Maria Karnilova, Julia Migenes, Leonard Frey and Pia Zadora.

He got his start on television in 1966, playing the part of Dr. Nick Hunter #1 on Search for Tomorrow. Later soap opera roles were on The Secret Storm and How to Survive a Marriage. His film credits include The Seven-Ups with Roy Scheider and Tony LoBianco plus F.I.S.T. with Sylvester Stallone. In 1976 he co-starred in 2 episodes of The Adams Chronicles as James Madison.

Kercheval is most well known for his role as Cliff Barnes on the CBS television series Dallas. He starred in the show from 1978 to 1991, from pilot episode to series finale. He initially was cast as Ray Krebbs before being given the role of Cliff Barnes. Kercheval and Larry Hagman were the only Dallas cast members to stay with the series throughout its entire run, although Kercheval's character was only a recurring character during the first two seasons. He became a regular cast member in the 1979-1980 season. Kercheval reprised the role of Cliff Barnes in the 1996 Dallas reunion, J. R. Returns, and he appeared in the 2004 CBS reunion special. He again reprised the role in the Dallas (2012) series.

In the 1980s, he made numerous appearances on Super Password and The $25,000 Pyramid. In 1991, he appeared in the reunion movie, I Still Dream of Jeannie, playing Mr. Simpson, a guidance counselor at Anthony Nelson Jr.'s high school and was the temporary master for Anthony's mother, Jeannie (Barbara Eden). This was because Larry Hagman, who played Tony Nelson, was not available to reprise his role, as he had not yet finished his run on Dallas. He also appeared as a ballroom dance Teacher in the independent film California Casanova.

In 1985, he became a partner in the Old Capital Popcorn Company. The Business thrived at first but the partnership soured in 1988. The financial issues and other conflicts led to a 1989 armed rampage and suicide on the Dallas set by one of the partners.

In 2006, Kercheval appeared in a musical at Southampton's Mayflower Theatre and Plymouth's Theatre Royal in the performance of White Christmas playing The General. In 2007, he reprised his role at the Edinburgh Playhouse and the Wales Millennium Centre in Cardiff. He reprised his role in Sunderland in 2010. He also returned to his role playing The General in the White Christmas at The Lowry in Salford Quay with Corrie Star Wendi Peters and Brookside and Loose Woman Claire Sweeney from November 2012 till January 2013.

Ken Kercheval is a lung cancer survivor. He has five children from three marriages, all of which have ended in divorce. As of 2012, he has six grandchildren.