Brad Peacock's journey in Major League Baseball began when he was drafted by the Washington Nationals in the 41st round of the 2006 MLB Draft. His professional debut came in 2011 with the Nationals, where he showcased his potential as a pitcher. During his brief stint with the team, Peacock appeared in three games, starting two of them, and posted a 2-0 record with a 0.75 ERA, which hinted at his capabilities on the mound.

In December 2011, Peacock was traded to the Oakland Athletics as part of a multi-player deal. His time with the Athletics was primarily spent in the minor leagues, where he continued to develop his skills. Despite not making a significant impact at the major league level with Oakland, his performances in the minors kept him on the radar of other teams.

The Houston Astros acquired Peacock in February 2013, and it was with this team that he spent the majority of his MLB career. Over the years, Peacock transitioned between starting and relieving roles, adapting to the needs of the team. His versatility as a pitcher was evident as he contributed in various capacities, whether as a starter, long reliever, or setup man.

One of the highlights of Peacock's career came during the 2017 season. He played a crucial role in the Astros' pitching staff, appearing in 34 games and starting 21 of them. Peacock finished the regular season with a 13-2 record and a 3.00 ERA, helping the Astros secure a postseason berth. His efforts were instrumental in the Astros' journey to winning the World Series that year, marking a pinnacle in his career.

In the following seasons, Peacock continued to be a valuable member of the Astros' pitching rotation and bullpen. He was known for his ability to deliver in high-pressure situations, often being called upon to stabilize games. Injuries, however, began to affect his playing time and performance in the later years of his career.

Peacock's tenure with the Astros concluded after the 2020 season. In 2021, he signed minor league contracts with the Cleveland Indians and the Kansas City Royals, but he did not make a significant impact at the major league level with either team. His career in MLB was characterized by adaptability and moments of brilliance, particularly during the Astros' championship run.