Richard Hopwood Thornton was born in 1845 in Didebury, Lancashire, England, and was the son of William L. Thornton, a prominent English Wesleyan clergyman and Latin tutor. After attending New Kingswood School near Bath, Richard H. Thornton passed the entrance examination for Oxford University in 1862, but instead entered a London business house. After a visit to Paris in 1870, he went to Canada in 1871; there, he taught school in various places. Receiving a small legacy from his mother in 1874, he traveled throughout North America, attended the Columbia University law school in Washington, and was admitted to the bar in Philadelphia in 1878. The previous year, he had married Martha Sproul, with whom he had one child, who died in infancy.

In 1884, Thornton received an invitation from Judge Matthew P. Deady to come to Oregon and serve as the first dean of the University of Oregon law school. Thornton accepted the position and held the post in Portland for the next 19 years. After his retirement in 1903, he traveled in Europe with his wife, and after her death he moved to London in 1907. There, he compiled the work "An American Glossary," which was published in 1912. He returned to the U.S. in 1916 and eventually took up residence again in Portland, Oregon, where he died in January 1925.