He was a son of Bryan Donkin and worked in this father's company in Bermondsey, primarily on paper-making equipment.
He married Caroline Hawes, granddaughter of William Hawes, notable as founder of the Royal Humane Society.
Caroline Hawes was the sister of Sir Benjamin Hawes, brother-in-law of Isambard Kingdom Brunel.
John Donkin was the father of Bryan Donkin Junior and grandfather of Sydney Donkin.