William Mercer Green (July 12, 1876 – November 12, 1942), was the 4th Bishop of Mississippi from 1938 till 1942.

He was the grandson of William Mercer Green, the 1st Bishop of Mississippi.

[2] He also served as rector of St John's Church in Knoxville, Tennessee.

His last post prior to his election was as rector of St Andrew's Church in Jackson, Mississippi.

His funeral was held on November 16 and was presided over by R. Bland Mitchell, Bishop of Arkansas.