Brother of H. C. Hansen (by whom his work was influenced), he was trained in Copenhagen, where the dominant figures were C. F. Hansen (no relation) and G. F. Hetsch, who imparted a robust Neo-Classicism to the aspiring architect. In 1838 Hansen went to Greece, where he joined his brother in Athens, designing the Demetrios House (1842–3—later a hotel, but demolished 1958), and later the Academy of Sciences (1859–87) and the National Library (1859–91). In 1846 he settled in Vienna at the invitation of Förster, whose daughter he later (1851) married. Influenced by French Neo-Classicism, by the architecture of Schinkel, and by his studies of Greek Antique and Byzantine architecture, he created many of the most distinguished buildings of his time in Vienna. He collaborated with Förster on Byzantino-Rundbogenstil designs for the Army Museum in the Arsenal (1850–6), and contributed to the developments on the Ringstrasse, including his masterpiece, the Parliamentsgebäude (Parliament Building—1874–83), a handsome composition in the spirit of Greek Antiquity with some of the finest Greek Revival interiors ever conceived. After a visit to Italy in 1856 his style turned to a luxuriant Italian Renaissance (e.g. Protestant School, Karlsplatz (1859), and the Heinrichshof on the Ringstrasse (1861), which set the Cinquecento flavour of many apartment-blocks on the Ringstrasse over the following years). However, Hansen also became a leader in the use of polychromy, influenced no doubt by Semper, and synthesized Greek and Renaissance themes in his beautiful Musik-vereinsgebäude (Hall of the Music Society—1869–70) and Academy of Fine Arts (1872–7), Vienna.
Anzeiger der österreichischen Akademie der Wissenschaften, cxiv (1977), 260–76;Lhotsky (1941);Middleton & Watkin (1987);Niemann & Feldegg (1893);Russack (1942);Strobl (1961);Traulos (1967);Wagner-Rieger (1970, 1980)