Born in Scotland where he received his education, Rev, Allan, after serving for some time in the ministry in his native land, migrated to Australia. There he devoted his energies mainly to special evangelistic work for which he had a particular aptitude. After moving to the U.S.A., charges in New York City and Boston were served with distinction. On a visit to Toronto, in connection with a series of evangelistic services, he made initial contact with the Canadian Church, which led to his association with the Presbyterian Church in Canada after Union.
Since he was not a minister of the Canadian Church, he could not be formally called to St. Paul's. It was arranged that he be placed in charge of this pastorate as stated supply for a one year term. Prior to that period he was received and enrolled as a minister of the Church, a call regularly presented and accepted, and in February 1926 Rev. Wm. Allan was inducted into the charge of St. Paul’s.
Following the disturbing events of the preceding year – with regard to church union creating The United Church of Canada – he guided the congregation through six strenuous and unsettled years. At this point Rev. Allan accepted a call to a wider field of service at Dovercourt Rd. Presbyterian Church and terminated his ministry with St. Paul's on the 1st September 1931. While pastor of the new charge in Toronto, he greatly enhanced his prestige as a preacher with the well received radio program, "Morning Devotions".
The Rev. Wm. Allan was, unfortunately, drowned at sea, a victim of the sinking of the liner Athenia on 3rd September 1939, in the North Atlantic, the first British ship to be sunk by a German U-boat in World War II. Rev. Allan had, as attested by witnesses, laboured long in the task of saving others, before being lost when his lifeboat capsized.
His son, Andrew, who later became well known as the national head of CBC Radio Drama from 1943 to 1955, along with his fiancée, Judith Evelyn, the American stage and screen actress, were among those who survived.