Endicott Howard Peabody was an American politician from Massachusetts. A Democrat, he served a single two-year term as the 62nd Governor of Massachusetts, from 1963 to 1965. His tenure is probably best known for his categorical opposition to the death penalty and for signing into law the bill establishing the University of Massachusetts Boston. After losing the 1964 Democratic gubernatorial primary, Peabody made several more failed bids for office in Massachusetts and New Hampshire, including failed campaigns for the U.S. Senate in 1966 and 1986.

The 1966 United States Senate election in Massachusetts was held on November 8, 1966. Republican incumbent Leverett Saltonstall retired after serving for 22 years. Republican Massachusetts Attorney General Edward Brooke defeated Democratic former Governor of Massachusetts Endicott Peabody in a landslide.