William Swan Plumer (July 26, 1802 – October 22, 1880) was an American clergyman, theologian and author who was recognized as an intellectual leader of the Presbyterian Church in the 1800s.

William S. Plumer was born to William and Catharine Plumer (née McAlester) in Greersburg, present day Darlington, Pennsylvania, on July 26, 1802.

He graduated from Washington College (now Washington and Lee University in Virginia) in 1825, received his religious education at Princeton Theological Seminary in New Jersey, and was ordained in the Presbyterian Church. He was licensed in the Presbytery of New Brunswick, a Presbytery in New Jersey, as a clergyman in 1826, and the state's Orange Presbytery ordained him as an evangelist in 1827.

Plumer was the minister of several churches during his career, most notably: First Presbyterian Church, Richmond, Virginia (1834 –1846); Franklin Street Presbyterian Church, Baltimore, Maryland (1847–1854); Central Presbyterian Church, Allegheny, Pennsylvania (1854–1862); Arch Street Presbyterian Church, Philadelphia, Pennsylvania (1862–1865); and Second Presbyterian Church, Pottsville, Pennsylvania (1865–1867).