Born at Hope River, Prince Edward Island, on June 24, 1871, McNally moved with his parents to Summerside as a young child. Here he completed his high school education in 1886, receiving a scholarship and the Governor-General’s silver medal. He graduated from the Prince of Wales College, Charlottetown in 1889, with an honour’s diploma, a teacher’s certificate and another silver medal. He taught for a year before gaining a Bachelor of the Arts and a Licentiate in Philosophy from the University of Ottawa in 1892. He became one of the first students at the Canadian College in Rome. In 1893 he gained a Doctorate in Philosophy and in 1897, a Doctorate in Theology. He was ordained by Cardinal Cassetta in the Archbasilica of St. John Lateran on April 4, 1896 for the Diocese of Ottawa.
On his return to Canada McNally was curate at St. Patrick’s Church, Ottawa until in February, 1900 he went to Portland, Oregon as secretary to Archbishop Christie. In 1904 McNally returned to Rome for a further two years of study.
In December 1905 he was appointed pastor St. Stephen, Old Chelsea in Quebec and in 1909 he acted as notary to the first Plenary Council held by the Catholic Church in Canada. In May 1911 he was appointed pastor at St. Mary’s, Almonte, Ontario.
McNally was notified on April 4, 1913 of his appointment as Bishop of Calgary. He was consecrated at the Canadian College in Rome by Cardinal Falconio and was installed on Sunday, July 28, 1913 in the Cathedral in Calgary by Archbishop Emil Legal of Edmonton, after which there was a large reception. Bishop McNally was the first Irish bishop appointed in the Prairie Provinces.
On January 18, 1916 McNally sailed from New York to Rome in secret to submit the question of his dismissal of the Oblate Order from Sacred Heart Parish, Calgary to the jurisdiction of the Sacred Consistorial Congregation, which judged his case favourably. He returned on July 18 and proceeded in releasing four French Orders from his Diocese. Although the Oblates remained he had asserted his own authority.
On August 29, 1924 Bishop McNally was transferred to the Diocese of Hamilton as Coadjutor to Bishop Dowling, who died that day. McNally was Bishop of Hamilton for 13 years until 1937 when he was appointed to the Archdiocese of Halifax. McNally died on November 18,1952.