John William Donaldson (7 June 1811 – 10 February 1861) was an English academic and writer in Greek classics, a philologist and a biblical critic.

He was born in London, and was educated at University College, London, and Trinity College, Cambridge, of which he subsequently became a fellow. In 1841 he was elected headmaster of King Edward's School, Bury St Edmunds, but, "spectacularly unsuccessful", in 1855 he resigned his post and returned to Cambridge, where his time was divided between literary work and private tuition.

He is remembered as a pioneer of philology in the UK, though much of his work is now obsolete. The New Cratylus (1839), the book on which his fame mainly rests, was an attempt to apply to Greek the principles of comparative philology. The same year he was ordained deacon and in 1849 was graduated from Trinity College, Cambridge as a Doctor of Divinity. It was founded mainly on the comparative grammar of Franz Bopp, but a large part of it was original, Bopp's grammar not being completed ten years after the first edition of the Cratylus. In Donaldson's Varronianus (1844) the same method was applied to Latin, Umbrian and Oscan. He began a Greek dictionary, which was to have been the great work of his life and which he left unfinished apparently dying of mental stress of overwork, simultaneously being a tutor at Cambridge University and examiner at the University of London. When advised to take six months' rest he replied that this would cost him £1500. He spent his final four weeks moved to London however unable to conduct the students' examinations in his role as examiner.