About 1870 (based on college matriculation)
Montgomery was the son of Harvey Gibson and Isabelle Grant Crawford of Martinsburg, Pennsylvania.
He attended the West Sunbury Academy, graduating in 1888. He entered the University of Wooster in 1889, and graduated in 1893. For a year he traveled in the American west with several college friends, and in the autumn of 1894 entered Princeton Theological Seminary, graduating in 1897. He was chosen class poet in the Academy and in the University, and in his senior year, was elected toastmaster for Princeton’s annual Pan-Hellenic Banquet.
Upon leaving the seminary, Gibson was asked to accept the pastorate of the church at Atlantic Highlands, New Jersey, in 1897. On January 5, 1898, he was elected by the First Presbyterian Church of Wilmington, Delaware. Then, on May 17, 1898, he became pastor of the Roxborough Presbyterian Church in Philadelphia, Pennsylvania, serving there through at least 1904.