[4] McGuigan attended Prince of Wales College in Charlottetown from 1908 to 1911, winning the Governor General's Academic Medal in his final year.

[2] McGuigan was ordained a priest on May 26, 1918, by Bishop Henry Joseph O'Leary, at his childhood parish of St. Augustine's Church in South Rustico.

[4] However, the 1918 influenza pandemic forced the school to temporarily close in October 1918 and McGuigan himself fell ill, eventually recovering but losing much of his hearing.

[8] At Regina, McGuigan was confronted with a bleak situation: James Anderson had been elected Premier of Saskatchewan the previous year with the support of the anti-Catholic Ku Klux Klan;[9] the Great Depression had left two-thirds of the Saskatchewan population on welfare;[10] and McGuigan's predecessor as Archbishop, the late Olivier Elzéar Mathieu, had left the Archdiocese with $1.2 million in debt.

[4] During his four years in Regina, McGuigan also held the first Eucharistic congress in western Canada, organized religious vacation schools, and established the Catholic Federated Charities.

"[14] During the war, he released priests to serve as military chaplains and formed 90 women's societies to send parcels overseas.

[1] He supported foreign aid to Europe in order to stop the spread of communism, and he condemned the arrest and trial of Cardinal József Mindszenty in Hungary.

[2] McGuigan was created Cardinal-Priest of Santa Maria del Popolo by Pius XII in the consistory of February 18, 1946.

[2] Feeling the toll of his heavy workload, McGuigan requested a coadjutor bishop to take charge of diocesan affairs and eventually succeed him, and he received Archbishop Philip Pocock from Winnipeg in 1961.