He started practicing traditional functionalistic architecture, but over the years his professional interests changed to focus mainly on lighting which is what he is most famous for. He also expanded his field of occupation into areas of writing, becoming a journalist and an author. For a short period at the beginning of WWII, he was the head architect of the Tivoli Gardens project in Copenhagen. But like many other creative people, he was forced to flee Denmark during the German occupation but soon became a vital part of the Danish colony of artists living in Sweden.
His lifelong collaboration with Louis Poulsen began in 1925 and lasted until his death in 1967. To this day, Louis Poulsen still benefits from his genius. Poul Henningsen was also the first editor of the company magazine "NYT". The CEO of Louis Poulsen at the time, Sophus Kaastrup-Olsen, gave the magazine to PH as a gift after he had been terminated from another Danish newspaper - his opinions were too radical.
Poul Henningsen's pioneering work concerning the relationship between light structures, shadows, glare and color reproduction, compared to man's need for light, remains the foundation of the lighting theories still practiced by Louis Poulsen.