In the Senate, Cannon was known as a moderate in the Democratic Party. He served as chairman of several committees, including the rules committee and the inaugural arrangements committee. Cannon was nearly defeated for re-election in 1964 by Republican Lieutenant Governor Paul Laxalt in one of the closest election in history. However, he became more popular over the next few years and won re-election in 1970 with nearly 58% of the vote. In 1976, he faced U.S. Representative David Towell, who served just one term in the U.S. House of Representatives before running for the U.S. Senate. Cannon won re-election with 63% of the vote, one of his best election performances of his career. He won every county in the state, except for Eureka County, which Towell won with just 51% of the vote.