William Mortimer may refer to:
William Mortimer (rugby union) (1874–1916), English rugby union forward William Mortimer (architect) (1841/42–1913), English architect William Mortimer (cricketer) (1833–1916), English cricketer and British Army officer William James Mortimer (died 2010), publisher, president and editor of the Deseret News William Chapman Mortimer (1907–1988), Scottish novelist