John Croft was educated at the Hackney Church of England school, and through life held earnest religious views.
After spending five years (1855–60) as surgeon to the Dreadnought seamen's hospital ship, he returned to St. Thomas's to become demonstrator of anatomy and surgical registrar.
Croft was one of the earlier hospital surgeons in London to adopt the improved methods advocated by Lister.
His name is chiefly associated with the introduction of 'Croft's splints,' which were plaster of Paris cases made with scrubbing flannel and shaped to the limb.
They were employed in place of the ordinary splints and the 'gum and chalk' bandages which had previously been used in the treatment of fractures of the leg.