Beaver was born in Laramie, Wyoming. His parents are Dorothy Adell and James Norman Beaver, Sr. a minister. His father was of French and English heritage. His mother has Scottish, German, and Cherokee ancestry, and is a descendant of senator, governor, and three-time U.S. Attorney General John J. Crittenden.

His mother has Scottish, German, and Cherokee ancestry, and is a descendant of senator, governor, and three-time U.S. Attorney General John J. Crittenden.

He and his three younger sisters all attended Irving High School (where he was a classmate of ZZ Top drummer Frank Beard), but he transferred in his senior year to Fort Worth Christian Academy, from which he graduated in 1968.

He is most familiar to worldwide audiences as the gruff but tenderhearted Bobby Singer in Supernatural.

He also played Whitney Ellsworth on the HBO Western drama series Deadwood. Role of Whitney Ellsworth brought him acclaim and a Screen Actors Guild Awards nomination for Ensemble Acting after three decades of supporting work in films and TV.

He also worked as a newscaster and hosted jazz classical music programs on radio station KCSC.

Jim Beaver made his professional stage debut in October 1972, while still in October 1972, while still a college student, in Rain, from W. Somerset Maugham's short story, at the Oklahoma Theatre Centre in Oklahoma City, Oklahoma.

He starred in the television series Thunder Alley as the comic sidekick to Ed Asner, and as homicide cop Earl Gaddis on Reasonable Doubts.

In 1989, following a four—year courtship, Beaver married actress/casting director Cecily Adams, daughter of Get Smart star Don Adams. Couple's daughter Madeline was born in 2001. Cecily Adams died of lung cancer March 3, 2004.

He played a role opposite Nicolas Cage in the 2002 film Adaptation.