Student, Phillips Exeter Academy, 1918. Student, Weslyan University, Middletown, Connecticut, 1921. Doctor of Laws, George Washington University, 1927.
Degree (honorary), University New Hampshire. Degree (honorary), University Vermont. Degree (honorary), Belknap College.
Degree (honorary), New England College.
While in college, he served as a clerk to the New Hampshire State Senate. He became a lawyer after attending The George Washington University Law School and practiced law in Lebanon, New Hampshire. Cotton was elected to the New Hampshire House of Representatives again in 1943, and served as majority leader that year and as Speaker during 1945-1947.
In 1946 Cotton was elected to the United States House of Representatives from New Hampshire for the first time.
He served until 1954 when he ran for a seat in the United States Senate from New Hampshire in a special election to fill the vacancy caused by the death of Charles West. Tobey. He was elected to a full term in 1956, reelected twice and served in the Senate until 1975.
One of his most controversial votes came when he was the only senator from New England to vote against the Civil Rights Acting of 1964. However, Cotton would vote for later civil rights acts such as the Voting Rights Acting of 1965 and the Civil Rights Acting of 1968.
He was a prominent leader of his party in the Senate, chairing the Senate Republican Conference from 1973 to 1975.
He did not run for reelection in 1974. Three days before his final term ran out Cotton resigned to allow the governor to appoint Louis C. Wyman. Cotton was reappointed to the Senate in August 1975 after the election of his successor was contested.
The closest Senate election in history, it went through two recounts at the state level, followed by protracted debate on the Senate floor, until both candidates agreed to a special election.
Cotton served as a temporary senator until the September 1975 special election, the result of which was not challenged. Cotton returned to Lebanon, New Hampshire.
Cotton died on February 24, 1989, (age 88 years, 289 days) in Lebanon. He is interred at School Street Cemetery, Lebanon, Grafton County, New Hampshire.
The comprehensive cancer center at Dartmouth-Hitchcock Medical Center in Lebanon is named for him, and the federal building in Manchester, New Hampshire, also bears his name.
There is a historical marker in Warren, New Hampshire, which was unveiled in 2012, and says his rise from humble beginnings embodies the American way of life.
He also served as a member of the New Hampshire House of Representatives in 1923 as one of the youngest legislators in history.
Married Ruth Isaacs, May 11, 1927 (deceased 1978). Married Eleanor Coolidge Brown, 1980.