James Markham Marshall Ambler was born on December 30, 1848, at the Dell in Fauquier County, the second of four sons and second of five children of Richard Cary Ambler, a physician, and Susan Marshall Ambler. At age sixteen Ambler joined the 12th Virginia Cavalry Regiment and served during the closing months of the Civil War. He attended Washington College in Lexington from 1865 to 1867 and the University of Maryland School of Medicine in Baltimore, from which he graduated in 1870.
Ambler practiced medicine for four years before joining the U.S. Navy in 1874 as an assistant surgeon. His duty assignments included service aboard the screw tug USS