He graduated from LaSalle University in 1948, was admitted to the bar in 1949, and began to practice in Boothbay Harbor. Tupper also began to serve in local government; he was elected to the Boothbay Harbor board of selectmen in 1948, and was selected to serve as chairman in 1949. As a selectman, he took a lead role in creating the town's police department, and his other initiatives included adopting the secret ballot for election of town officials, competitive bidding for town equipment and services, and the town manager form of government.