U.S. architect, perhaps the greatest architectural renderer of his time; he was less known but more important as a master of the Romanesque Revival style initiated by H.H. Richardson (Richardson, Henry Hobson) and as an early designer of skyscrapers (skyscraper) ascribed to other architects.

Dismissed from the U.S. Military Academy, West Point, N.Y., Ellis may have completed his education in Europe. He worked as a draftsman for Richardson in Albany, N.Y., and then practiced architecture with his younger brother, Charles Ellis, in Rochester. His best work was done from 1885 to 1893 in St. Paul and Minneapolis, Minn., and in St. Joseph and St. Louis, Mo. The Noyes Brothers and Cutler Building, St. Paul (1886; J. Walter Stevens, nominal architect), strongly resembles the later Walker Warehouse, Chicago (1888), a Richardsonian structure designed by Louis Sullivan (Sullivan, Louis).

Ellis designed a 26-story skyscraper (1887; unexecuted) that would have been the first really tall building of steel-frame (framed building), or skeleton, construction in the world. This design was claimed by the Minneapolis architect Leroy Sunderland Buffington, who also asserted inaccurately his priority over William Le Baron Jenney of Chicago as the inventor of metal-skeleton construction suitable for tall office buildings. Another of Ellis' unexecuted designs was a small bank (c. 1888; published by Buffington in 1891) that might have been taken for one of the banks built by Sullivan in the Middle West from 1907.