In 1935, he was elected District Attorney of Washington County, a position his father had also held.
During World War II, he served as a captain in the United States Army.
In 1964, the phrase "under God" in the Pledge of Allegiance was challenged as a violation of the constitutional separation of church and state.
His decision was upheld by the New York Court of Appeals and the United States Supreme Court declined to review the decision, effectively leaving Justice Gibson's ruling as the law of the land.
On September 15, 1969, Gibson was appointed by Governor Nelson A. Rockefeller to the Court of Appeals to fill the vacancy caused by the resignation of Kenneth Keating.