He attended Harvard University, where he received a Bachelor of Arts degree in 1937.
During college, he played on the football, rugby, and soccer teams and was president of the Rocky Mountain Club. He received a law degree from Harvard Law School in 1941. During World World War II, Haskell served in the United States. Army from 1941 to 1945, seeing action in Asia and reaching the rank of major.
Following his military service, he was admitted to the bar in 1946 and moved to Denver, Colorado, where he worked as a tax lawyer
In 1964, Haskell was elected as a Republican to the Colorado House of Representatives from Arapahoe County, serving until 1969. In 1970, he left the Republican Party and became a Democrat in protest of President Richard Nixon"s invasion of Cambodia.
In 1972, Haskell decided to challenge three-term Republican incumbent Gordon L. Allott for a seat in the He defeated state Senator Anthony F. Vollack (later chief justice of the Colorado Supreme Court) in the Democratic primary. He defeated his closest competitor, Senator Allott, by less than 10,000 votes while President Richard Nixon carried Colorado by over 267,000 votes.
Haskell was sworn into the Senate on January 3, 1973.
He supported the regulation of auto emissions, the Panama Canal treaties, and alternative sources of energy. In 1978, he was defeated for re-election by Representative William L. Armstrong, losing by a margin of 59%-40%. After his Senate career, Haskell established his residence in Washington, District of Columbia, where he practiced law before joining Common Cause and a bipartisan group of retired lawmakers calling for campaign finance reform and an end to congressional gridlock.
Haskell suffered a cerebral hemorrhage in 1994 after falling on ice near his home in Washington.
A member of the Democratic Party, he served as a United States. Senator from Colorado from 1973 to 1979. As a state legislator, he became assistant majority leader in 1967 and also served as chairman of the House Judiciary Committee and a member of the House Education and Finance Committees. He served as a member of the Senate Finance and Energy and Natural Resources Committees, where he earned a reputation as a tax reformer and advocate for the environment.