Sellstedt took a studio and began his career as a portrait painter. In 1850, he married Louise Lovejoy and they lived in New York City for a brief period of time; she died a few years later in Buffalo.
In 1853, Sellstedt visited Stockholm, but returned to Buffalo and married Caroline Scott in 1856. Their home became a center of artistic activity. Sellstedt helped to arrange an art exhibition in 1861 that led to the establishment of the Buffalo Fine Arts Academy; he served as its president in 1876 and 1877.
In 1872, Sellstedt sent his self-portrait to the National Academy of Design; it won a commendation from Daniel Huntington and led to his election as an associate. In 1875, he became a National Academician. Sellstedt was active in the Saturn and Liberal Clubs of Buffalo. In 1904, he published his autobiography From Forecastle to Academy: Sailor and Artist and in 1910, Art in Buffalo. Sellstedt died on June 4, 1911.