William T. Doyle (born May 8, 1926) is a retired American politician and author who served as a Republican member of the Vermont Senate. As a senator from the Washington Vermont Senate District from 1969 to 2017, he is the longest-serving state legislator in Vermont history. After being defeated for reelection, Doyle continued teaching at Johnson State College until retiring in 2018. The author of a 1984 book on Vermont political history, The Vermont Political Tradition, in 2018 he also published a second work, A Lasting Impression: Vermont Historical Articles and Local Politics.