Bart was born on January 19, 1977, at the Baltimore Zoo. When Bart was five weeks old and weighed five pounds (2 kg), he was adopted by Doug and Lynne Seus, who worked as animal trainers for films. The Seuses trained Bart using a reward and praise system. While still a cub, he appeared in the TV series The Life and Times of Grizzly Adams playing Adams' companion bear, Ben, as a cub.

After reaching adulthood, he subsequently made his film debut in the film Windwalker (released 1981). He grew to 9' 6" (2.90 m) tall and weighed 1,500 pounds (680 kg) throughout his life as an adult.

Bart's greatest recognition came when he starred in the title role of Jean-Jacques Annaud's 1988 French film, The Bear, playing an adult grizzly bear who befriends an orphaned cub and defeats Hunters. Annaud auditioned 50 bear actors from all over the world before selecting Bart for the role. In order to perform the role, Bart, trained by Seus, successfully learned several new routines and behaviors, including going against his natural abhorrence of a strange bear to accept the unrelated cub co-starring with him. Annaud remained impressed with Bart's performance even after being injured by Bart when Annaud, against trainers' orders, entered Bart's enclosure to pose for publicity photos. The Bear was a hit in both Europe and the United States, grossing over $31 million in the United States and over $100 million worldwide, and reportedly resulting in an Oscar nomination for Bart, which was unable to go forward because animal actors are precluded from receiving Academy Awards.

In 1998, Bart made an appearance at the 70th Academy Awards as part of a salute to animal actors. He presented an envelope to Mike Myers onstage.

Bart the Bear 2, an unrelated Alaskan brown bear cub born in 2000 and adopted by Doug and Lynne Seus shortly before Bart's death, was named for Bart and has sometimes been called "Little Bart". Bart the Bear 2 has followed in the footsteps of the original Bart, becoming an established animal actor and Vital Ground ambassador.

At the time of his death, he was filming the television documentary Growing Up Grizzly (2001) (also featuring Bart's namesake Little Bart), which was narrated by Brad Pitt, who had appeared with Bart in Legends of the Fall.