His first enterprise was a cigarette paper factory which commenced production in 1922.

Starting from the late 1920s, Demirağ began to invest his capital in the development of the Turkish railway network.

In 1945 he founded the first opposition party, which was named Milli Kalkınma Partisi (National Development Party), but his party failed to receive the required number of votes for entering the Turkish parliament in the 1946 and 1950 general elections, and was eventually dissolved in 1958, a year after his death.

Demirağ donated his airplanes to his flying school (Gök Okulu) in Yeşilköy, which he established for attracting the interest of young Turks in aviation.

The land upon which the school was built was later nationalized by the Turkish government in order to enlarge the neighbouring Yeşilköy Airport (Atatürk International Airport) which was originally established as a military air base of the Ottoman Air Force in 1911.