Adamson's major contribution to architecture came following World War II when his firm became one of the leaders in the development of the Mid-Century Modern style in Canada.

After that time, Adamson moved to Montréal to work for Shell Oil Company supervising the construction of a housing unit.

By the end of the War, however, he had begun to transition to working in the International Style, which would dominate the architectural practice for well over a decade.

The best example of Adamson's early modern work is the "Sun House," a Rosedale home designed for Clare Wood in 1944.

Significant projects of the era included the Savoy Plaza Apartments - for which in 1953 he won his first Massey Medal - and the James Crothers House - a sprawling Lawrence Park mansion.