In the summer of 1811, he accompanied Bishop Joseph-Octave Plessis, as secretary, on a pastoral visit to the Îles de la Madeleine and New Brunswick; and was ordained the following October.

[1] Father Gaulin was assigned to assist Bishop Alexander Macdonell as a curate in Glengarry County in Upper Canada.

In May 1815, Gaulin returned to Quebec in order to accompany Bishop Plessis on a pastoral visit to the missions on the Gulf of St Lawrence.

[1] In July, Plessis assigned Gaulin to be the first resident pastor of St. Ninian's parish in Antigonish, Nova Scotia, with responsibility for Margaree and Chéticamp, Cape Breton.

He subsequently transferred his base to Chéticamp and by October 1816 was serving the Acadians of that community and of Margaree, and the Scots living in the Bras d'Or Lake district.

Three potential candidates declined before Bishop Jean-Jacques Lartigue of Montreal suggested Gaulin.

Bishop Bourget brought Gaulin to Montreal and appointed Patrick Phelan as coadjutor of Kingston.