[3] Brewster is a former vice president for fraud management with Mellon Bank and mayor of McKeesport, Pennsylvania.

On November 2, 2010, Brewster won a special election to fill the remaining term of Senator Sean F. Logan, who had resigned his seat on August 24, 2010, to take a position at the University of Pittsburgh Medical Center.

In July 2020, Brewster organized a meeting with bar and restaurant owners and signed a letter to Governor Tom Wolf urging him to lessen the restrictions on them imposed during the COVID-19 pandemic.

[5] In January 2021, although Brewster narrowly defeated his opponent, Republican Nicole Ziccarelli, by 69 votes, the Republican-led State Senate refused to swear in Brewster for his fourth term, despite the fact that his win had already been certified by state officials.

In a bizarre move, Republican leaders voted to remove Fetterman from his presiding role and halt Brewster's seating.