Chapin joined American Motors in 1954 when the corporation was formed with the merger of Nash and Hudson. Later, he served as an assistant treasurer and a director at AMC. By 1964, he held the post of executive vice president in charge of international operations of AMC. Robert B. Evans, chairman of AMC, recognized the talents of Chapin and promoted him from an executive vice president to take his place as chairman of the board. The move was to increase the firm's operational efficiency at the start of a difficult time.