Rep. John Olver, D-Mass., right, gestures to the audience as other members of the state’s congressional delegation, including from left, John Tierney, Jim McGovern and William Keating, look on during a tribute to Olver at the Democratic State Convention in Springfield, Mass., in June 2012. Michael Dwyer/Associated Press

BOSTON — Former U.S. Rep. John Olver, a Democrat who represented western Massachusetts communities for more than two decades in Congress, has died. He was 86.

Olver served in both the Massachusetts House and Senate before winning a 1991 special election for the Congressional seat left vacant by the death of Republican Rep. Silvio O. Conte.

Olver would hold the seat until he opted not to seek reelection in 2012, after the state lost a seat in Congress and was forced to draw new districts. He was born in Pennsylvania but ended up living much of his life in Amherst in western Massachusetts.

Gov. Maura Healey said Olver dedicated his life to serving the people of western and central Massachusetts and that he always stayed true to his values. She ordered flags lowered to half-staff at all state buildings Friday.

“He was a strong advocate for affordable health care, abortion access, public transportation and rural communities,” the Democrat said in a written statement. “I will always be grateful for his kindness and his friendship. He will be dearly missed, and my heart goes out to his loved ones.”

Olver received a master’s degree from Tufts University and a doctorate from the Massachusetts Institute of Technology before joining the faculty of the University of Massachusetts-Amherst, ahead of entering politics.

In Congress he rose to become chair of the Appropriations Subcommittee on Transportation, Housing, and Urban Development, an influential committee that helped him bring federal dollars home to his district.

He was also known for his progressive politics, and for shying away from the spotlight.

Democratic U.S. Rep. James McGovern described Olver as a “humble public servant with the heart of an activist.”

Although the two were twice arrested in Washington, D.C. protesting the genocide in Darfur, Olver was committed to local issues such as clean energy, environmental protection and public transportation, McGovern added.

“His quiet demeanor and wry sense of humor concealed a razor-sharp understanding of the issues facing the American people and a deep faith in our ability to solve them together,” McGovern said in a written statement, calling Olver “my friend and longtime colleague.”

Olver’s wife Rose Olver died in 2014 at the age of 77.