He took courses at Burdett College after graduating from Charlestown High School and went into the advertising and public relations business.
Higgins resigned in 1937 to become chief justice of the Massachusetts Superior Court and Cotter ran to succeed him.
During the campaign, Cotter was criticized by opponent Joseph A. Langone Jr. for using Higgins' franking privileges to mail 40,000 letters on United States House of Representatives stationery in which Cotter stated that Higgins' office would remain open and referred to himself as "acting Congressman".
Cotter defended himself, stating that a new law allowed a Congressional office to remain open following a Congressman's resignation for six months or until a successor is chosen, and that the letter would not be an issue if he was not candidate.
[1] On June 1, 1953, Cotter was appointed commissioner of the Boston Fire Department by Mayor John Hynes.