Joseph Gillespie Armstrong (October 15, 1901 - April 23, 1964) was an American suffragan bishop of the Episcopal Diocese of Pennsylvania from 1949 until November 7, 1960, when he was elected coadjutor.

Armstrong served as rector of Severn Parish (a/k/a St. Stephens Crownsville) near Annapolis, Maryland,[2] and of Christ Church (Georgetown, Washington, D.C.), then as chaplain in the United States Navy in World War II.

Armstrong served several years as rector at St. Mary's Episcopal Church in Ardmore, Pennsylvania.

On April 1, 1964, Robert L. DeWitt, suffragan bishop of Michigan, was elected as his coadjutor, and became his successor.

Bishop Armstrong died at home in Bryn Mawr, Pennsylvania, survived by his second wife and daughters.