Hoagland was born in Omaha, Nebraska, and graduated from Omaha Central High School and then Stanford University in 1963. He was a first lieutenant in the United States Army from 1963 to 1965 during the Vietnam War. He graduated from Yale University Law School in 1968 and was admitted to the bar the same year. He set up practice in Washington D.C. as a clerk to Judge Oliver Gasch of the United States District Court for the District of Columbia from 1969 to 1970. He was a staff attorney in the District of Columbia public defender service from 1970 to 1973.
Hoagland was elected to the Nebraska Legislature in 1978 and served until 1986 when he declined to seek re-election. However, in 1988, when Hal Daub decided to run for the U.S. Senate, Hoagland ran for the open seat and was elected to serve in the 101st Congress. He was re-elected in 1990 and 1992. In 1994, he was defeated for re-election by Jon Christensen; his defeat was attributed to the Republican Revolution.
Throughout his terms in Congress, Hoagland was a strong advocate for the environment. In 1990, The League of Conservation Voters released a National Environmental Scorecard ranking members of Congress on their environmental voting records. Peter Hoagland scored a perfect 100%. He was a member of the Episcopal church, the American Bar Association, and Common Cause.
After leaving Congress in 1995, Hoagland lived in Washington, D.C., where he worked for a law firm.