Lancelot Mackenzie was born in West Calder, Scotland, on 1 June 1888 to George Mackenzie and Emma Mackenzie (maiden name unknown). He was the fourth of nine children, four sons and five daughters and a half-brother born in 1905. The family moved to Willington Quay in northern England about 1893. Mackenzie was a school teacher and is recorded as an uncertificated teacher in England in 1911.
Mackenzie appears to have emigrated to Australia with his parents sometime between 1911 and 1913, although no record of this journey is available. The family settled in Port Adelaide and later Port Pirie, South Australia. During 1913 and 1914 Mackenzie was a vocal soloist with the Port Adelaide Orpheus Society.
Mackenzie enlisted in the Australian Imperial Force (AIF) at Jamestown, South Australia, in May 1916 and was attached to the 50th Battalion, 4th Reinforcements. His unit embarked from Adelaide aboard the troopship Ballarat on 12 August 1916, arriving in Devonport, England, on 30 September 1916 before moving to the Codford training and transfer camp in Wiltshire. In December 1916 Mackenzie was sent to France with the 50th Battalion; in January 1917 he was admitted to hospital with acute rheumatism and was repatriated to England. In February 1917 he was moved to the 3rd Australian General Hospital in Brighton, England, and in April to the 1st Australian Auxiliary Hospital at Harefield Park. Mackenzie was transferred to a convalescent depot in Weymouth, England, in June 1917 and in September was returned to Australia aboard the troopship Ulysses. He was discharged on 12 December 1917.
Mackenzie re-enlisted in the AIF at Melbourne in May 1918 and was attached to the Australian Army Medical Corps, Sea Transport Section. He embarked from Sydney aboard the No.2 Hospital Ship Kanowna on 5 June 1918 and remained with the ship for its final two voyages as a hospital transport (9th and 10th) with its final return to Australia in March 1919. His position during this time is not documented. Mackenzie was discharged on 26 March 1919.
During the 9th voyage of the Kanowna, Mackenzie participated in a concert performance by "The Kanowna Follies" on 3 August 1918, singing "Somewhere a Voice is Calling".
Civil Registration records for England & Wales indicate Mackenzie married Gertrude Clarkson at Tynemouth, England in late 1918, during a period when the Kanowna was in dry dock in England for repairs from 25 November 1918 to 5 January 1919. The couple travelled back to England in late 1923 and again in 1930. Mackenzie settled in Victoria and is recorded as residing in the Melbourne districts of Camberwell, Auburn, and Hawthorn from 1928 to at least 1954; his occupation during this period is recorded as clerk.
Lancelot Mackenzie died at Heidelberg, Victoria on 27 May 1967 at the age of 78. He is listed on an honour board of the Port Adelaide Orpheus Society, located at the South Australian Maritime Museum. Gertrude Mackenzie died on 19 September 1961 at the age of 68. Both are buried in the Springvale Botanical Cemetery, Victoria.