William Sluman Messervy (August 26, 1812 – February 19, 1886) was an American trader on the Santa Fe Trail who in 1850 was elected to represent the New Mexico Territory in the United States House of Representatives, but did not take his seat. He later served as Secretary of the Territory and in 1854 was acting Governor of New Mexico. In 1854, Messervy returned to his home town, Salem, Massachusetts, where he was elected as Mayor and became a Justice of the Peace.