John King Ewing was the son of John K. and Ellen L. Ewing. The Ewing's were residents of Uniontown, Fayette County, PA. It was there that John began a career in the real estate business, but by 1884, he moved to Pittsburgh to continue his career.
The firm he established in 1884 became the John K. Ewing, Co., No. 64, Federal Street, Allegheny, with himself and cousin James C. Ewing as partners.
He married Mary B. Stockdale and they had at least one child, Mr. John Ewing II. John King Ewing died in 1904.