Born William McGibbon on October 13, 1876 in Halifax, Nova Scotia, Canada, he was the son of Bernard McGibbon and Mary Lawler. He went to St. Mary’s Retreat, Dunkirk, New York where he attended the Preparatory School. He then proceeded on to the Passionist novitiate in Pittsburgh, Pennsylvania. He professed his vows on July 2, 1894 and received the name Oswin. He was ordained to the priesthood by Bishop Henry Moeller of Columbus, Ohio on June 18, 1903 at Holy Cross Church, Mount Adams, Cincinnati, Ohio.
His first assignment was Vice-Master of Novices. Among other assignments he was Pastor of St. Mary’s, Dunkirk, New York. He was also Vicar of St. Michael’s, Hoboken, New Jersey in 1923. He served as Rector at Immaculate Conception Monastery, Jamaica, New York and from 1937 to 1944 was Rector of St. Gabriel’s Monastery, Brighton, Massachusetts.