Steen Eiler Rasmussen was born on 19 February 1898 in Copenhagen to Lieutenant colonel and later general Christian Rasmussen and Anna Dorthea (Dori) Jung. He first apprenticed as a mason and then studied architecture at the Royal Danish Academy of Fine Arts from 1916 to 1918. In 1919 he set up his own practice.

One of his most important books was London. It was first published in Danish in 1934, in English (as London, the Unique City) in 1937. When this edition was re-issued in 1948, Rasmussen had added two Postscripts: “For English readers only”, and “For American readers only”. A shorter version was published as a paperback in 1960.

On 15 June 1934 he married Karen Margrethe Schrøder (12 November 1904 – 31 March 1985), daughter of economist and later Danish National Bank manager Frederik Carl Gram Schrøder og Astrid Koefoed. He is the father of the linguist Una Canger. He was a close friend of the author Karen Blixen.

Rasmussen was a lecturer at the Academy from 1924 and became a professor in 1936. Among his students were Jørn Utzon, designer of the Sydney Opera House, and Marian Pepler who designed rugs for Gordon Russell in the 1930s .

A prolific writer, Rasmussen’s bibliography was published by librarian Finn Slente in 1973.