William Mansel may refer to:
- William Lort Mansel, an English churchman and academic, Master of Trinity College, Cambridge and Bishop of Bristol.
- William Mansel (MP for Gloucestershire), see Gloucestershire (UK Parliament constituency)
- Sir William Mansel, 7th Baronet (1670-c. 1732) of the Mansel Baronets
- Sir William Mansel, 9th Baronet (1739-1804) of the Mansel Baronets, MP for Carmarthenshire (UK Parliament constituency)
- Sir William Mansel, 10th Baronet (1766-1829) of the Mansel Baronets