He studied at the Athens School of Fine Arts (1894-1896) under Nikephoros Lytras and continued his studies in Paris under Benjamin Constant, Jean Paul Laurens and Jules Lefebvre. In 1900 he won an award at the International Exhibition of Paris. He settled in Greece in 1903 and in 1911 was appointed professor of sketching at the School of Fine Arts but resigned a few months later. In 1915 he was appointed anew and taught until 1949, while in 1946 he became the director of the School. In 1949 he was made a member of the Athens Academy and withdrew from the artistic scene because of an eye disease which did not permit him to exercise his art any longer.
Mathiopoulos painted symbolic, idealistic and historical subjects as well as scenes from everyday urban life, but he became particularly well-known and popular through his portraits. He primarily made use of pastels and, to a lesser degree, oil and having mastered impressionistic types, rendered his works with elegance and a tendency to idealize in agreement with the aesthetics of the Belle Epoque.