In Judea, a young Jewish man named Brian is born on the same day as, and next door to, Jesus Christ. Mistaken for the Messiah from birth, Brian's life takes a series of misadventures that lead him to become inadvertently involved with the Roman Empire. As he grows up, Brian seeks to break free from his oppressive Roman rulers and find his own path. His quest for personal freedom and identity is constantly thwarted, partly due to the societal and political turmoil of the time. His unintentional involvement with various groups and individuals, each with their own agendas, further complicates his life.

During his tumultuous journey, Brian finds himself mistaken for a prophet and unwittingly becomes the leader of a messianic movement. This attracts the attention of various factions, including the Romans and zealot revolutionaries, each seeking to use Brian for their own ends. As he navigates through a series of comedic and absurd misunderstandings, Brian's attempts to escape his unwanted messianic status lead to increasingly bizarre situations. His interactions with an array of quirky characters, including his overbearing mother, rival political activists, and eccentric followers, highlight the satire on religion, politics, and historical events of the era.