Mark Odom Hatfield was born in Dallas, Oregon on July 12, 1922 and was the only child of Charles D. and Dovie Odom Hatfield. He graduated from Salem High School and earned his undergraduate degree at Willamette University in 1943. A Navy Officer during World War II, he witnessed battles at Iwo Jima and Okinawa and was among the first servicemen to enter Hiroshima after the atomic bombing. Following his time in Japan, Hatfield was assigned to aid French troops in Vietnam.

After the war, Hatfield attended Stanford University and received his master's degree in political science in 1949. He returned to Salem and became an associate professor in the politics department at Willamette (1949-1956). He also served as dean of students at Willamette University from 1950 to 1956. While still teaching, Hatfield became a member of the Oregon House of Representatives (1951-1955), then the state Senate in 1955. Hatfield won the election for Oregon Secretary of State in 1957, and two years later became Oregon's 29th governor. He is the youngest person to serve in either office. In 1962, he was reelected as governor, becoming the state's first two-term governor in the twentieth century.

Senator Hatfield was first elected to the United States Senate in 1966. He served as Chairman of the Committee on Appropriations from 1981-1987, and again from 1995-1997, and was a member of the subcommittees on Commerce, Justice, State, and Judiciary; Energy and Water Development; Interior; and Labor, Health and Human Services, and Education. This role enabled Senator Hatfield to direct critical funds to Oregon projects, public works, and constituents. Senator Hatfield also served on the Committee on Rules and Administration, the Joint Committee on Printing, the Joint Committee on the Library, and the Committee on Energy and Natural Resources. Hatfield served five terms spanning 30 years in the U.S. Senate, becoming Oregon's longest-serving senator. His wartime experiences profoundly shaped his political views, and he was a vocal opponent of war and nuclear arms, an anti-abortion and anti-death penalty supporter, and an advocate for federal spending on medical research.

Senator Hatfield was also a prolific writer and author of Not Quite So Simple (1967), Conflict and Conscience (1971), Between a Rock and a Hard Place (1976), Against the Grain: Reflections of a Rebel Republican (2000), and co-author of Amnesty: The Unsettled Question of Vietnam (1976), The Causes of World Hunger (1982), Freeze! How You Can Help Prevent Nuclear War (1982), and What About the Russians? (1984).

Hatfield spent 46 years of his life in public service before retiring in 1997, having never lost an election during his long political career. He was the seventh most senior Senator and the second most senior Republican at the time of his retirement. He then resumed his teaching career, serving at Willamette University, Portland State University, and George Fox University. He held more than 80 honorary degrees.

Mark O. Hatfield died on August 7, 2011 at the age of 89. He was survived by his wife, the former Antoinette Kuzmanich, and their four children and seven grandchildren.