Brentwood, located approximately 6 miles (10 km) from downtown Pittsburgh and is 101 years old, was once an integral part of Baldwin Township, which included the villages of Brentwood, Point View, and Whitehall.

In 1914, a group of citizens in the village of Brentwood took a set of grievances to the Baldwin Township Board of Commissioners, regarding the lack of sidewalks, sewers, fire protection, police, and a school house. Upon further disregard of these necessities from the township, a group of men from the village held a meeting on January 27, 1915, to discuss secession. After considerable discussion, the boundary lines of Brentwood were finalized by the Board of Trade. Building a sidewalk along Brownsville Road was the first official action taken by the Board of Trade. On November 6, 1915, the Quarter Sessions Court of Allegheny County decreed that Brentwood was officially seceded from Baldwin Township. The proceedings to incorporate were filed on May 15, 1916, creating the Borough of Brentwood.

On December 4, 1915, special elections were held to elect a burgess, auditors, justices of the peace, high constable, tax collector, assessor, and councilmen. Brentwood's first burgess was Bernard Kestner, sworn in on December 9, 1915. He served Brentwood for sixteen years. The board met monthly and continued to discuss necessary steps for the structure of the borough.

On Labor Day, 1928, the borough celebrated the official opening of the park, pool, and paving of Brownsville Road.

The population was 10,082 at the 2020 census.