Born in Northumberland County, Pennsylvania, Witmer obtained an Artium Baccalaureus degree from Central Pennsylvania Business School (now Central Penn College) in 1883.
Subsequently, he pursued a legal career, gaining admission to the bar in 1887.
His legal expertise extended to the national stage when he assumed the role of Assistant Attorney General for the Spanish Treaty Claims Commission from 1902 to 1904.
[1] On February 20, 1911, Witmer was nominated by President William Howard Taft to a seat on the United States District Court for the Middle District of Pennsylvania vacated by the impeachment and conviction of Judge Robert W. Archbald.
Witmer was confirmed by the United States Senate on March 2, 1911, and received his commission the same day.