From 1933, in the wake of Atatürk's secularist reform of the Turkish university system, Koçu taught history in the high schools of Alman, Kuleli, Pertevniyal and Vefa in Istanbul.

He had lost the family mansion he inherited from his father, as well as his money to create Istanbul’s “grand register.” The exact location of his grave could never be determined.

[1] Koçu's best known work is his Istanbul Encyclopedia (İstanbul Ansiklopedisi), which evokes many different aspects of the ancient city, including many stories from Ottoman times.

In 1973, financial difficulties forced Koçu to interrupt composition at the eleventh volume, while still working on the letter G.[2] The text is accompanied by fanciful line illustrations.

[4] After a seven-year hiatus, the Istanbul Encyclopedia resumed publication on July 15, 1958, with the support of a businessman named Mehmet Ali Akbay.

In the Turkish edition of National Geographic Magazine in 2002, and later in the book Istanbul: Memories and the City, writer Orhan Pamuk identified Koçu as "homosexual."

In a response to Pamuk's work, the historian Murat Bardakçi also identified Koçu as homosexual, but stated he belonged to a specific category of male sexual subjectivity known as cemal aşığı, a "lover of facial beauty.

"[7] In his book, Istanbul Encyclopedia (İstanbul Ansiklopedisi), Koçu included multiple references to queer and transgender people throughout the Ottoman Empire.