William Markle Berlin (March 29, 1880 – October 14, 1962) was an American businessman and politician who served as a Democratic member of the U.S. House of Representatives from Pennsylvania for two terms from 1933 to 1937.
He was engaged as an automobile distributor, in the wholesale oil and gas business, and in coal mining.
After his time in Congress, he served as clerk of the court of Westmoreland County, Pennsylvania, from 1937 to 1941.
He was a delegate to the 1944 Democratic National Convention in Chicago, and an unsuccessful candidate for the Republican congressional nomination in 1950.
He served as assistant librarian of the United States House of Representatives from February 1, 1957, until 1961 when promoted to librarian, and served in that capacity until his death in Greensburg, Pennsylvania.