He graduated from Dartmouth College in 1968, then worked for the Peace Corps in rural Panama.

[2] After returning to the United States, he attended then graduated the Antioch School of Law in 1975.

[6] Guernsey represented the same district in the 1985–1986 Massachusetts legislature, winning in an uncontested election.

[9] In 1991, Guernsey attempted to run for Massachusetts Senate, but lost to Jane Swift, who won 52% of the vote.

In connection with that campaign he sought an advisory opinion from the Federal Elections Commission before borrowing funds from his home or bank account, both of which were jointly owned with his spouse, who approved of these transactions.