Grassley lived in Iowa during his early life. He entered politics immediately after college, serving in the Iowa state legislature from 1959 until 1974, when he was elected to the United States House of Representatives, of which he was a member from 1975 to 1981, being reelected in 1976 and 1978. He was elected to his senate seat in 1980, defeating the Democratic incumbent, John Chester Culver, who had only served one term. Grassley was reelected in 1986, 1992 and 1998.
Grassley is particularly interested in issues relating to families and senior citizens, and has worked with Democrats on bipartisan bills supporting these groups. He has been chairman of the finance committee since 2003 and was also its chairman from January to June 2001.