Brought to the United States at age eight, Dielman grew up in Maryland. He attended Baltimore's Calvert College, Roman Catholic institution where his father taught music, graduating in 1864. While still in school, he began producing illustrations of Civil War battle scenes. In 1866 Dielman took a job as cartographer with the United States Engineering Office. He worked on topographic surveys in the Alleghany Mountains and surrounding area until 1872. During this period, he followed C.Y. Turner's antique classes at the Maryland Academy in Baltimore. After quitting his government job, Dielman went to Munich, studying under Wilhelm von Diez at the Royal Academy. There he encountered fellow Americans, J. Frank Currier, Frank Duveneck, and Walter Shirlaw. Like his compatriots, Dielman visited the Bavarian town of Polling in summers to do outdoor work, and he also enjoyed hiking in the Alps. He made a trip to Vienna in 1875.
The Philadelphia Centenniel Exhibition drew Dielman home in 1876. He settled in New York, sharing a studio with the painter, Harvey Young. Soon after his arrival, he helped found the Society of American Artists, serving as its treasurer, 1878-79, and secretary, 1880-82. Although much of the basis for the Society's founding had been objection to the Academy's jurying practices, in the ranks of the Society, Dielman spoke out for tolerance and understanding of the older men of the National Academy. His role as moderate continued after his election to the Academy; and later, as Academy president, he pushed for, and accomplished the merger of the two organizations, arguing that the Academy needed an infusion of "new blood" from the Society (NAD Minutes, May 9, 1906).
Dielman's first American success came with his initial appearance of his work in an Academy annual exhibition in 1877; his full-length A Patrician Lady--Sixteenth Century recieved considerable attention. Yet he still found it necessary to supplement his income with illustration work in Scribner's and Century magazines and numerous books. In 1886 he became the lecturer in perspective at the Academy school, a position he retained to 1930. Later, he taught at the Art Students League; the City College of New York, where he was Professor of Descriptive Geometry and Art; and the Cooper Union, where he directed the art department.
In addition to his easel painting and illustration work, Dielman painted murals, designed mosaics, and etched (he was a founder of the New York Etching Club). In the Academy his greatest contribution was as an influential participant in the management of its affairs. He was first elected to the Council in 1886, and was reelected to that service in 1887 and 1888; from 1890 to 1892 he was Academy treasurer; in 1896 he was returned to Council membership, serving three years, and then was elected president. In 1899, when he was selected for the presidency over Thomas Waterman Wood, Dielman became the first foreign-born Academician to hold the post. Following ten years in that office, he was again elected to Council for three years. Dielman was, therefore, active in Academy administration with only brief interruptions over a period of twenty-seven years.
