He was the son of John Oberholtzer, a former schoolteacher who during Ellis' lifetime ran Willowdale Mills (now The Mill at Anselma in Chester Springs, Pennsylvania) and later became a successful grain merchant. Ellis' mother, Sara Louisa Vickers Oberholtzer, was a respected poet and social activist known for her work in abolition, post-Civil War social reform, and equal rights. Ellis had one brother named Vickers Oberholtzer.
Ellis was educated at the University of Pennsylvania (Ph. D., 1893), at German universities (Berlin and Heidelberg), and in Paris. He was on the editorial staff of the Philadelphia Evening Telegraph (1889–96), editor of The Manufacturer (1896-1900), and literary and dramatic editor of the Philadelphia Public Ledger (1902–08). He edited the American Crisis Biographies (20 volumes) and in 1908 and 1912 directed historical pageants at Philadelphia. His wife, Winona McBride Oberholtzer, was the sister of publisher Robert M. McBride.