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).
[3][4] 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.
[5] 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.