At the beginning of the American Revolutionary War, he was commissioned first lieutenant in the Pennsylvania "Flying Camp". On September 10, 1776, he was captured at the surrender of Fort Washington on November 16, 1776, and worked at the blacksmith trade while a prisoner. He was later put aboard the prison ship Judith and was subsequently imprisoned in New York City's Old City Hall. He was paroled on board ship December 10, 1777.
Pennsylvania Senate and Congress
Brown was a member of the Pennsylvania State Senate from 1783 to 1787, and was elected as a Democratic-Republican to the Fifth Congress to fill the vacancy caused by the resignation of Samuel Sitgreaves. He was reelected to the Sixth and to seven succeeding Congresses, serving from December 4, 1798 to March 3, 1815. He was not a candidate for renomination in 1814, and retired from public life and lived on his farm.