Dillingham was born in Shutesbury, Massachusetts on August 10, 1799, a son of Paul Dillingham Sr. and Hannah Dillingham. The Dillingham family moved to Waterbury, Vermont in 1805, where Dillingham worked on the family farm and attended the district school in Waterbury and Montpelier's Washington CountyGrammar School. In 1820, he commenced studying law in the office of Judge Daniel Carpenter. He was admitted to the bar in March 1823, and in April he began to practice in Waterbury as Carpenter's partner. He gained a reputation throughout Vermont as a skilled trial lawyer with a superior ability to present oral arguments to judges and juries.
Increasingly opposed to slavery and secession, Dillingham declined the Democratic Party's 1860 nomination for governor. When the American Civil War started, he officially changed his allegiance from Democratic to Republican. He served as the 22nd Lieutenant Governor from 1862 to 1865. Holding office at the height of the war, Dillingham's efforts were focused on aiding governors Frederick Holbrook and J. Gregory Smith to obtain passage of laws for raising, paying, and equipping soldiers for the Union Army. In addition, he campaigned throughout Vermont for the Republican ticket of Abraham Lincoln and Andrew Johnson in the 1864 United States presidential election.
Governor
Dillingham served as the 29thgovernor of Vermont from 1865 to 1866. As governor, he created Vermont's first reform school and established Vermont's first normal school for teacher training. It also fell to Dillingham to appoint two members of the U.S. Senate to replace senators who had died. To succeed Jacob Collamer, Dillingham selected Luke P. Poland. To replace Solomon Foot, Dillingham first offered the appointment to former governor J. Gregory Smith. When Smith declined, Dillingham selected George F. Edmunds.
Later life
He resumed the practice of law, and was a delegate to the State constitutional convention in 1870. He retired in 1875.
Death and burial
Dillingham died at his home in Waterbury on July 26, 1891. He is interred in the Village Cemetery in Waterbury.
Family
He married Sarah Partridge Carpenter, a daughter of Daniel Carpenter. She died on September 20, 1831, and on September 5, 1832 Dillingham married Sarah's sister Julia. He had seven children who lived to adulthood, including William Paul Dillingham, who served as governor and U.S. Senator. Dillingham was also the father in law of Senator Matthew H. Carpenter.