William Lewis Dewart (June 21, 1821 – April 19, 1888) was a Democratic member of the U.S. House of Representatives from Pennsylvania.

He was graduated from Dickinson Preparatory School in Carlisle, Pennsylvania, and from Princeton College in 1839.

He studied law, was admitted to the Northumberland County, Pennsylvania, bar in 1843, and commenced practice in Sunbury.

He served as chairman of the United States House Committee on Revisal and Unfinished Business.

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