[1][3] After his ordination, the diocese sent Harkins to Rome to study theology and canon law at the Pontifical Gregorian University.

[3] He received his episcopal consecration on April 14, 1887, from Archbishop Williams, with Bishops Patrick O'Reilly and Lawrence McMahon serving as co-consecrators, at the still unfinished Cathedral of SS Peter and Paul in Providence.

[3] At that time, the Diocese of Providence also included the Cape Cod region of Massachusetts, along with the islands of Nantucket and Martha's Vineyard.

[1] Harkins in 1889 consecrated the Cathedral of SS Peter Paul, which had been started by his predecessor, Bishop Thomas F. Hendricken, in 1878.

[7] During Harkins' tenure, the diocese grew to be one of the largest in the country, with a high percentage of Catholics in the general population.

He purchased property in Providence and invited the Dominican Province of St. Joseph religious order to come to the diocese and operate it.