[5] McGrath was loaned to the Diocese of Portland, Maine, where he was made an assistant at St. Joseph Church in Old Town and did missionary work among Native Americans on the Penobscot Indian Island Reservation.
[1] A visit to the Pacific Northwest brought him into contact with Bishop Edward John O'Dea, who needed more English-speaking priests in the Diocese of Seattle and appointed McGrath as an assistant at St. James Cathedral in 1904.
[7] In addition to his pastoral duties, McGrath was named a diocesan consultor in 1910 and dean of the counties of Pierce, Thurston, and Grays Harbor in 1915.
[9][10] However, Brady declined the appointment and Pope Benedict XV instead named McGrath as bishop on December 21, 1918, the twenty-third anniversary of his priestly ordination.
[11][12] With only one parochial school in the entire diocese at the beginning of his tenure, McGrath mandated that the Confraternity of Christian Doctrine be established in every parish and mission.