Duncan Smith was educated at Bishop Glancey Secondary Modern, Solihull, until the age of 14, and then at , a Merchant Navy training school on the Isle of Anglesey, until he was 18. There, he played rugby union in the position of fly-half alongside Clive Woodward at centre. In 1973, he spent a year studying at the University for Foreigners in Perugia, Italy. He then attended the Royal Military Academy Sandhurst and was commissioned into the Scots Guards as a second lieutenant on 28 June 1975, with the Personal Number 500263. He was promoted to lieutenant in the Scots Guards on 28 June 1977. During his service, he served in Northern Ireland and Southern Rhodesia (now Zimbabwe), where he was "aide-de-camp" to Major-General Sir John Acland, commander of the Commonwealth Monitoring Force monitoring the ceasefire during elections. He retired from the army on 2 April 1981, moving to the Regular Army Reserve of Officers. He ceased to belong to the Reserve of Officers on 29 June 1983.