After emigrating to the United States, in 1819 he was appointed as the pastor of St Peter's in New York and as the Vicar General of the diocese under Bishop John Connelly, O.P.
In the summer of 1827, Irish immigrants working the Enfield Falls Canal at Windsor Locks, Connecticut, sent to New York for a priest to tend to one of their number who had fallen grievously ill.
From there he went to New Haven, and having missed the boat for New York, stayed over and said Sunday Mass for a group of Catholics at a building on the Long Wharf.
[3] In 1829 he again found himself in charge of the diocese (with fellow cleric Felix Varela) when Dubois travelled to Europe to gather funding and support for his restructuring plans - a mission that lasted 2 years.
During his time in New York, Power founded the Catholic newspaper the Truth Teller, was active in the Irish Emigrant Society, raised funds and championed the opening of an orphanage.