Emerson was a member of the Democratic Party throughout his career, until changing to the Republican Party on May 18, 2004.
While in Congress, Emerson represented Missouri's 8th congressional district from 1981 until 1993, and Missouri's 7th congressional district from 1993 to 2013. He served as the House Minority Whip from 1995 to 1999, and as the 52nd Mayor of Cape Girardeau, Missouri from 1959 to 1963. He was also a businessman and owned several radio stations in Missouri.