1945–47, he was teaching assistant with Professor Kaare Klint at the Royal Danish Academy of Fine Arts' School of Architecture, Copenhagen.

His work has been featured in one-man exhibitions in Zurich, London, New York City, Stockholm, Paris and Copenhagen, and his many awards for design include the Eckersberg Medaillen (1950) and the C.F.

During his time with Kaare Klint, Mogensen fostered a deep commitment to producing classical, simple and highly functional furniture.

Continuing Klint's innovative studies in how the size and proportion of objects should influence their design, Mogensen, collaborating with Grethe Meyer, produced a project in 1954 called the Boligens Byggeskabe (Construction Cupboards of the House), which introduced the idea of building shelving and storage units as part of a room, rather than purchasing and placing them in the space.

Mogensen did studies to determine the standard measures for common objects, such as cutlery and shirts, and how many of each item the average person owned.

By the end of the decade, however, Mogensen had re-embraced a more straightforward functionalism that Klaus Meedom, writing about the Cabinetmaker's exhibit, said was "so strict that he has to violate his own rules to be able to breathe freely."