During his term as Coadjutor Archbishop, Msgr. Gauthier founded no less than thirty-seven parishes.
He welcomed seventeen religious communities into the diocese and canonically erected four more: the Institute of the Sisters of Notre-Dame-du-Bon-Conseil (1923), the Société des Missions-Étrangères (1925), the Oblates franciscaines de Saint-Joseph (1929), the Filles réparatrices du Divin-Cœur (1929).
In May 1933, he called for the holding of a diocesan Synod.
He successfully led the creation of the diocese of Saint-Jean-de-Québec (1933), which became the diocese of Saint-Jean-Longueuil, the fifth diocese to be separated from the original diocese of Montreal.
Msgr. Georges Gauthier died at the Hôtel-Dieu in Montreal on August 31, 1940 at the age of 68.
A few days before his death, he confessed to his priests during their annual retreat his fear, not of “old age, but of ageing” and acknowledged that he had entered “the novitiate of death”.
In accordance with his last wishes, his remains were placed in a modest wooden coffin covered with a simple black cloth. No funeral oration was pronounced during the funeral at the Cathedral. Then the coffin was taken to the funeral chapel of the bishops that he had built between 1930 and 1933.
According to canonical rule, he was titular archbishop of Montreal for less than a year: eleven months and ten days. Chronological reality shows us, however, that his episcopal service in Montreal was 28 years, 17 of which as Archbishop with full powers.
In less than a year, the diocese lost three bishops: Msgr. Paul Bruchési, who died on September 20, 1939, Msgr. Emmanuel-Alphonse Deschamps, an auxiliary, who died on June 23, 1940, and Msgr. Georges Gauthier, who died on August 31, 1940.