Ian was the son of Thomas Huddart Donking by his second wife, Isabella Lundie. Thomas Donking was a ship owner of Middlesbrough, in partnership with R.A. Constantine.

When war was declared in 1914, the Constantine and Pickering Steamship Company owned twenty-two ocean-going steamers and six coasters. A separate division of the company, known as RA Constantine & TH Donking operated the coastal ships, transporting coal down the east coast of Britain. Donking was a cousin of J Warley Pickering who owned a ship chandling company.

Ian was educated at Winchester from 1932 and Matriculated in 1937. He was Captain of the University Boxing.

Somewhat unusually, whilst at Winchester, he had been commissioned as a Second Lieutenant in the Green Howards (TA) in August 1936. This meant that he was saluted on Corps days by men in the school on parade

On 24 August 1939, he was promoted to Lieutenant in the 4th Battalion The Green Howards, his local regiment. He was promoted to Captain.

He was a Major when he was killed by enemy action aboard a ship off Tobruk on 10 May 1942.

He is commemorated on the Alamein Memorial Column 59 and on the Memorial at the Royal Military Chapel, Sandhurst.