Bob Brenly's journey in Major League Baseball began when he was drafted by the San Francisco Giants in 1976. He made his debut with the team in 1981, stepping into the role of catcher. Brenly quickly became known for his defensive skills behind the plate and his ability to handle pitchers effectively. His tenure with the Giants spanned nearly a decade, during which he became a reliable presence both on the field and in the clubhouse.

In 1984, Brenly had one of his best seasons, earning a spot on the National League All-Star team. That year, he posted a .291 batting average with 20 home runs and 80 RBIs, showcasing his offensive capabilities. Despite being primarily a catcher, Brenly occasionally played at third base, demonstrating his adaptability on the field.

One of the most memorable moments of Brenly's playing career occurred on September 14, 1986, in a game against the Atlanta Braves. In a single inning, Brenly committed four errors while playing third base, a rare and challenging feat. However, he redeemed himself by hitting a game-winning home run later in the game, exemplifying his resilience and ability to overcome adversity.

After leaving the Giants in 1989, Brenly had brief stints with the Toronto Blue Jays and returned to the Giants before retiring as a player in 1989. His transition from player to coach was seamless, as he joined the Giants' coaching staff shortly after retiring. Brenly's understanding of the game and his leadership qualities made him a valuable asset in his new role.

In 2001, Brenly took on the role of manager for the Arizona Diamondbacks. In his first season as manager, he led the team to a World Series championship, defeating the New York Yankees in a thrilling seven-game series. This victory marked the Diamondbacks' first World Series title and solidified Brenly's reputation as a capable leader.

Brenly continued to manage the Diamondbacks until 2004. After his managerial career, he transitioned to broadcasting, where he provided color commentary for various networks, including Fox and the Chicago Cubs' broadcasts. His insights and experience as a former player and manager enriched his commentary, making him a respected voice in the baseball community.