Andrew Duncan Bett was born at Frankston, Victoria, on 20 October 1888 to parents David Millye Bett and Mary Theresa Bett (née McArthur). Bett had four half-sisters and two half-brothers born to a previous marriage of his father to Elizabeth Wilson, who died in 1884.
Electoral records from 1912 show his occupation as actor and at the time of his enlistment Bett stated his occupation as chorister.
Bett enlisted in the Australian Imperial Force in Melbourne on 2 August 1915 and was attached to the 8th Battalion, 13th Reinforcements. He embarked for Egypt with the rank of private on 29 December 1915 aboard the troopship Demosthenes. He was based at Serapeum, Egypt until 26 March 1916, when Bett was transferred to France, disembarking at Marseilles on 31 March 1916. In August 1916, Bett received a gunshot wound to the arm while in action and was hospitalised. He rejoined the 8th Battalion on 11 January 1917.
On 20 August 1917, Bett was attached to the 1st Australian Divisional Concert Party, The Sentimental Blokes, and remained with the concert party until 18 January 1919. Bett performed as a tenor with the concert party, which presented a typically vaudeville style entertainment for troops in the field in France and Belgium. Bett is identified in a performance by The Sentimental Blokes in Belgium during 1918, at which he sang “I hear you calling me” and performed in the short sketch, “Chiselling”.
Bett embarked for Australia aboard the troopship City of Poona on 28 March 1919. He disembarked at Melbourne on 14 May 1919. During this voyage, Bett forfeited 10 days’ pay for breaking ship at Colombo on 21 April 1919. He was discharged on 6 July 1919.
Bett married Annie Winifred Cummings in Sydney in 1920. The couple had a son, Brian Robert Bett, born in Sydney in 1923.
After his discharge, Bett appears to have continued a singing career for a time. First as a tenor and then as a baritone, with some acting. From about 1924 to 1927, Bett was performing on radio. In April 1924, he performed with the Newcastle City Council Concert Band at the Newcastle Amphitheatre in New South Wales.
From about 1930, Bett appears to have been employed as a clothing examiner and was living in Glenmore, New South Wales. In February 1942, Bett was an employee at the Randwick Auxiliary Hospital in New South Wales.
Andrew Duncan Bett died at Parramatta, New South Wales in 1958 at the age of 70.