Duncan Kennedy emigrated to Australia from Scotland sometime before 1913, at which time he was living in Toowoomba with his younger brother William and playing soccer with Corinthians.
He later married Ida Denyer in Woollahra, New South Wales in 1914, and it was in that state he enlisted in November 1915. Kennedy was first seen with the 56th Battalion at Ferry Post at the Suez Canal in April 1916, where he caught influenza. He soon recovered and was sent from Egypt to France in June. A month later, Kennedy received a gunshot wound to the thigh and was evacuated to England.
He spent the next 18 months serving at several bases in England including Perham Downs and Hurdcott before returning to France to rejoin the 56th Battalion in March 1918. He remained in France until March 1919, and embarked for Australia in May.
Kennedy returned to Toowoomba after the war, joining his brother William in the Returned Soldier’s Soccer Club, later known as Diggers. He played there for one season before moving to Brisbane where he joined Wynnum. The Toowoomba Chronicle reported on 31 August 1923 that Kennedy was to be briefly reunited with old teammates when his Wynnum team visited Toowoomba to play a representative side. His brother William was mooted to line up against him.
Kennedy later became president of Bulimba Rangers soccer club and was still in the role when he died in 1951. The Queensland Times of 24 July 1952 reported that the Duncan Kennedy Shield was inaugurated in his honour and was presented to the winner between the Brisbane and Ipswich U16 representative teams over several years.