The former building senator of the Prussian city of Altona, Gustav Oelsner was relieved of his duties in 1933. As a progressive urban planner and architect, a member of a social democratic senate and the son of Jewish parents, Oelsner became persona non grata after the National Socialists came to power. Through the mediation of architect friend Fritz Schumacher and at the invitation of the Turkish Ministry of Labour, he managed to emigrate to Turkey in 1939, where he was employed until his departure from the country in 1949 as an expert in national urban development in Ankara.

Oelsner became the founding father of urban planning in his country of exile. He worked in a leading position on the "Committee for Technology and Urban Planning" [Şehircilik Fen Heyeti] at the Ministry of Public Works, which was founded in 1939, and as a professor of urban planning at the only two universities for the training of architects. He was also the author of numerous articles for the architectural journal Arkitekt and published numerous essays in which he revealed himself to be a consistent advocate of cautiously modernising urban planning.

In Turkey, Oelsner was confronted with a new challenge: establishing urban design in a country with growing cities and a society in transition. After the abolition of the sultanate, Kemalist Turkey was confronted with the establishment of a new political culture that also demanded new architecture. Oelsner was tasked with restructuring towns large and small according to hygiene and sanitary requirements, finding the best possible locations for schools in the pursuit of literacy, and developing squares in which the old religious centres were replaced by administrative and court buildings, cultural centres and sports facilities. His expertise was also sought after a major earthquake in Erzincan in 1939, when large areas needed to be rebuilt with earthquake-proof buildings.

Oelsner was intensively involved in the planning of villages and small towns in the province. He studied traditional village structures, and talked to the inhabitants and the mayors to find out what they needed. He looked at traditional, primitive forms of ventilation and sun protection to reflect on what could be adopted for use in the present. His pencil and camera were ever-present tools which he used to record his observations and conversations.

The first two weeks of each month Oelsner worked in the urban planning office in Ankara, while, during the second half of the month, he taught at Istanbul Technical University and the Academy of Fine Arts Istanbul. In Ankara he rented a flat in central Karanfil Sokak, but letters addressed to him at the Konak Hotel in Istiklal Caddesi in Beyoğlu suggest that he lived there when in Istanbul. The Konak Hotel is the former Grand Hotel Tokatlıyan, built by Alexandre Vallaury, where Trotski resided for some time in the late 1920s. Founded in 1897 by the Armenian Mıgırdıç Tokatlıyan on what was then Rue de Pera, the luxury hotel was taken over in 1919 by the Serb Nicolai Medowitsch, then in the 1940s by the Turkish businessman Ibrahim Gültan, who changed the name to Konak Hotel. Oelsner had a 30-minute walk from the Konak Hotel to Istanbul Technical University.

As a professor of urban planning, Oelsner had an unique impact on the education of young architects in Turkey for almost ten years. From 1940, he was entrusted with establishing a chair of urban planning at the TU and he worked there alongside colleagues such as Clemens Holzmeister, Paul Bonatz and Rudolf Belling. From 1943, Oelsner also taught at the Academy of Fine Arts. The aim of Oelsner's teaching programme was to raise entire ranks of responsible young urban planners who would serve their country primarily as building officials in rural regions. His teaching was aimed at this future task of the students and was based on his own urban planning practice. Oelsner's teaching was informed by the knowledge and experience gained from his travels through Turkey. It was only through Oelsner's activities that urban planning moved into the focus of architectural education. For many years, there was no awareness of the urgency of a theoretically sound, detailed examination of urban planning. It was only Oelsner's work and the involvement of later important urban planners such as Kemal Ahmet Arû, Orhan Alsaç and Gündüz Özdeş that raised awareness of the problem.

Although Oelsner was recognised and in demand as an urban planner in Turkey, he intensified his contacts with his homeland from 1946 onwards. A lively correspondence developed between him and old political companions and colleagues, and finally Oelsner decided to remigrate to Hamburg as a consultant for reconstruction planning (Wiederaufbauplanung) in 1949. He did not return to Turkey until 1955, when he was invited to sit on a panel of judges for the “City Plan of Ankara” competition. In the summer of the same year, he received an honorary doctorate from Istanbul Technical University. Gustav Oelsner died only one year later, in Hamburg.