Larson was born in Westwood, California, the son of Viola (née Baum) and Earl Larson. He was raised in McCook, Nebraska.

Larson plays guitar; he has claimed his early experiences as a musician led to his concerns about occult and destructive influences in rock music. He would later incorporate his guitar playing into some of his sermons. In the 1960s, the focus of Larson's preaching centered mainly on the leftist political ideology, sexually suggestive lyrics, Eastern religious mysticism, and antisocial behavior of many of the era's rock musicians. Less flamboyant than the Peters Brothers and less sensational than Jack Chick, Jeff Godwin, or Jacob Aranza, Larson is still remembered as one of the most vocal fundamentalist Christian critics of rock music.

By the 1970s, however, much of Larson's teachings concerned Satanism. Larson originally rejected Christian rock music based on its similarity in sound and image to secular rock music. Larson frequently appeared as a guest on secular and religious talk shows.

"Talk Back" with Bob Larson

In 1982, Larson launched "Talk Back", a two-hour weekday call-in show geared mainly toward teenagers and frequently focused on teen-oriented topics such as role-playing games and rock music. By this time Larson had come to embrace contemporary Christian music, including styles such as heavy metal and rap, and actively promoted the music and artists on his show.

By the late 1980s, in what would come to define his later ministry, Larson was often heard performing exorcisms of callers on the air. The subjects of Satanism and Satanic ritual abuse were frequent topics of discussion. Death metal performer Glen Benton of Deicide became a regular caller.

Larson tried his hand at writing fiction: Dead Air (1991) was largely ghost-written by Lori Boespflug and Muriel Olson. His later novels Abaddon (1993) and The Senator's Agenda both linked Satanic ritual abuse to political corruption; the latter was largely written by Larson and his second wife. However, a former vice president of BLM (Bob Larson Ministries), Lori Boespflug, claimed that much of Dead Air, though presented as Larson's work, is actually her own. Supporting these claims is a letter from Larson's lawyer that warns Larson of his "potential liability to Lori", anticipating that "the role Lori has played" would lead her to "demand recognition and/or profit participation" in respect to Dead Air and its sequels.

In 2004, Larson returned to the radio airwaves after a two-year absence with a daily talk show heard on a network of radio stations and simulcast and archived on the Internet.

Today, Larson remains active. His ministry professes to offer an alternative counseling outlet to people who have problems with violence, self mutilation, multiple personality disorders, Satanic ritual abuse, or molestation.