When Adolf Hitler gained power in Nazi Germany, Berger found work in Prague. However, his cartoons upset Hitler and he was forced to flee the country. After spells in Budapest and Paris he arrived in London in 1935 where he worked for the Daily Telegraph. He drew a series of celebrity caricatures for Sunday Dispatch. His work also appeared in Life Magazine, The Picture Post, The New York Times, The New York Herald Tribune and Le Figaro.
Mark Bryant has pointed out: "In addition he (Berger) produced posters for the theatre and worked in advertising for the Post Office, Shell, London Passenger Transport Board, Wolsey Socks, Gillette and others. Berger was held in such high esteem that many celebrities (including Roosevelt, Churchill, Garbo, Pavlova, Chaplin, Dietrich, King Victor Emmanuel) actually sat to have their caricatures drawn."
After the Second World War Berger moved to the United States and became a naturalized citizen of the country in 1955.
Oscar Berger died on 15th May, 1997.