After an initial training as a painter in Flensborg, Hansen attended the Academy in Copenhagen from 1842 until 1846, where he concentrated on decorative painting. Like Købke (q.v.), Hansen was involved with the painted decorations of the Thorvaldsens Museum in Copenhagen. He traveled frequently, for example, to Germany in 1847, and in 1850 left for an extensive two-year European journey, visiting Spain, France, Belgium, the Netherlands, and Great Britain. Later, in 1868-69 and 1875, he visited Italy. For many years he taught perspective and ornamental design at the Copenhagen Academy and was a member of numerous artistic committees inside and outside of this institution. As a consequence, Hansen became an influential figure in the Danish art world. From 1868 through 1890 he was the artistic director of the Copenhagen porcelain manufacturer Bing & Grøndahl. He strongly advocated the aesthetic enhancement of industrial products. Because of his premier position as a designer and his interest in the Renaissance, Danish art of a historic bent predominantly leaned toward a neo-Renaissance style. As a painter, Hansen was the first Danish artist to specialize in architectural painting. He received rapid fame for his detailed and harmonious depictions of buildings and richly decorated interiors, often in the Renaissance style. His minute studies of Frederiksborg Castle were used for the reconstruction of its interior after the fire of 1859. Hansen was also involved with the rebuilding of the famous Neptune fountain by the sculptor Adriaen de Vries (ca. 1546-1626) at Frederiksborg, which had been dismantled during the Swedish occupation in 1659.