Costin served eight years on the Lynn City Council before being elected mayor in 1956.
[3] As mayor, he proposed and spearheaded an urban renewal plan which targeted the Brickyard neighborhood of Lynn in an effort to make the city more attractive to industry and give it the ability to compete with surrounding communities' shopping malls but the program ultimately failed to deliver on its promises.
[4] Costin was a Kennedy delegate to the 1960 Democratic National Conventions.
[5] He was reportedly a finalist for the position of United States Postmaster General in 1976.
[6] In late 2018, the Post Office building in which Costin served as postmaster[5] was renamed in his honor by an Act of Congress.