He successfully ran for the Massachusetts House of Representatives in 1998, representing the 9th Norfolk District for three terms. Brown again moved up the ladder of state politics to the state Senate in March 2004 when he won a special election to replace Democrat Cheryl Jacques. Brown was re-elected for a full term in November 2004, and again in November 2006, running without opposition the second time. He won re-election in November 2008, defeating Democratic candidate Sara Orozco by a 59–41 percent margin. Following his re-election, Brown was one of five Republicans in the 40-seat Massachusetts Senate. In the Massachusetts Senate, Brown served on committees dealing with consumer protection, professional licensing, education, election laws, public safety, and veterans' affairs.