Karahan, who was born in İstanbul in 1929, started his career in Yapı Kredi Bank in 1946. After leaving the Head Office of Yapı Kredi, he worked as a member of the Board of Directors of Sabancı Holding and the General Coordinator of Sabancı Holding.
Since 1975 Karahan had been working in top level positions such as General Coordinator of various Sabancı Companies including Akbank and the Holding itself, member of the Board of Directors, Vice-Chairman of the Board of Directors, Managing Director, and Chairman of the Board of Directors. In addition to being a member of the Board of Directors of the Holding and the Chairman of the Audit Committee, Karahan was also a member of İSO.