James G. Jenkins was born at Saratoga Springs, N.Y., July 18, 1834, the son of Edgar Jenkins, a merchant, and Mary Elizabeth (Walworth) Jenkins. His mother's father was Reuben Hyde Walworth, a justice of the Supreme Court of New York and a distinguished Chancellor of that state.
James was educated in the private schools of his native city and began the study of law in the offices of Ellis, Burrill, and Davison, New York City. Upon his admission to the bar he immediately commenced the practice of his profession and two years later, in 1857, removed to Milwaukee.
Jenkins was law partner with several distinguished firms in Milwaukee and at the time of his appointment to be United States district judge for the eastern district of Wisconsin (July 2, 1888), he was generally recognized as the leader of the bar. When Walter Q. Gresham resigned the office of United States circuit judge for the seventh judicial circuit to become a member of President Cleveland's cabinet (March 1893) Jenkins was appointed to succeed him and continued to serve in that capacity until his retirement to private life in 1905.
After his retirement from the bench, Jenkins was for seven years (1908-1915) dean of the law school of Marquette University, Milwaukee. Jenkins was of medium height, commanding presence, and distinguished bearing, and enjoyed to an unusual degree a deserved popularity with the people of his state. He died August 6, 1921, in Milwaukee.