The City of Walnut is a General Law city incorporated on January 4, 1959. It is governed by the City Council/City Manager form of government. A five-member City Council is elected by the Residents, and a Mayor is elected by the Council to serve a twelve-month term. Walnut's City Manager is appointed by the Council to oversee the daily activities of the city.

Tom Weiner was appointed City Manager of Walnut on February 1, 2022. As the City Manager, Mr. Weiner serves as the Chief Administrative Officer of the City and is responsible for providing the City Council with policy recommendations and implementing them as adopted; while providing effective municipal services in accordance with City Council policies and the Walnut Municipal Code. He is also responsible for the overall planning and control of all day-to-day operations, including oversight of the City's adopted annual Budget, programs, and City services. These comprise of Community Services, Community Development, Finance, Public Works, and management of all contract services, which includes police services provided through the Los Angeles County Sheriff’s Department. 

Mr. Weiner, who holds a Bachelor of Science degree in Public Administration from California State University Dominguez Hills, has over 33 years of municipal experience. He previously served the cities of Santa Fe Springs, Norwalk, Signal Hill, and Lake Elsinore prior to his service with the City of Walnut (which began in 2010). He served as Community Development Director and subsequently Assistant City Manager in Walnut prior to his appointment to City Manager in 2022.