In 1958 Time–Life opened a branch in Turkey, and Güler became its first correspondent for the Near East. Soon he received commissions from other international media, such as Paris Match, Stern and the London Sunday Times. In the 1960s, Güler's photographs were used to illustrate books by notable authors and were displayed at various exhibitions throughout the world. His works were exhibited in 1968 in 10 Masters of Color Photography at the New York Museum of Modern Art and at Photokina Fair in Cologne, Germany. His photo album Türkei was published in Germany in 1970. His photos on art and art history were used in Time, Life, Horizon and Newsweek magazines and publications of Skira of Switzerland. Güler traveled on assignment to such countries as Iran, Kazakhstan, Afghanistan, Pakistan, India, Kenya, New Guinea, Borneo, as well as all parts of Turkey. In the 1970s he held photographic interviews with such notable politicians and artists as Winston Churchill, Indira Gandhi, Maria Callas, John Berger, Bertrand Russell, Willy Brandt, Alfred Hitchcock, Ansel Adams, Imogen Cunningham, Marc Chagall, Salvador Dalí and Pablo Picasso. Some critics consider his most renowned photographs to be his melancholic black-and-white pictures taken mostly with a Leica camera in Istanbul, mainly in the 1950s and 1960s, a golden age of photojournalism. Güler's work is collected by international institutions, such as the National Library of France in Paris; the George Eastman Museum in Rochester, New York; University of Nebraska-Lincoln Sheldon Memorial Art Gallery; Museum Ludwig Köln, and Das imaginäre Photo-Museum, Köln.