Sven Gottfrid Markelius (25 October 1889 - 24 February 1972) was a Swedish modernist architect. Markelius played an important role in the post-war urban planning of Stockholm, for example in the creation of the model suburbs of Vällingby (1950s) and Farsta (1960s).
Born in Stockholm, he attended the Royal Institute of Technology and the Academy of Arts in Stockholm from 1910 to 1915, later working at the offices of Ragnar Östberg and Erik Lallerstedt. He developed an early interest in housing and planning, was one of the founder members of CIAM in 1928, and participated in the modernist housing section of the Stockholm International Exhibition (1930), the birth of Swedish Functionalism.
In 1931, he co-authored the book-length manifesto "acceptera", promoting modernism as a set of cultural values. His association with Swedish reformer Alva Myrdal (1902-1986) resulted in a design for a 57-unit communal-living Collective House in the center of Stockholm, in 1935. The building offered communal amenities like childcare facilities and shared kitchen and meeting spaces, all at least partly inspired by the Narkomfin Building in Moscow. Markelius lived in the Collective House himself for thirty years, serving as an unofficial handyman, to make sure the building still worked, and to demonstrate his commitment to the values of social housing.
Meanwhile, among his major civic projects, Markelius began work on the Concert Hall in Helsingborg in 1932. In 1952, Markelius was nominated to the board of design consultants for the United Nations Secretariat Building by Sweden. Towards the end of his career the architect turned his attention to city planning.