Arriving in Paris in 1934, Jahan left behind a banking career to work in the graphic arts and photography. By 1936, he was exhibiting and in 1937 was included in a group exhibition of prominent Parisian photographers such as Man Ray, Laure Albin-Guillot and Rogi Andre. As an editorial photographer, he joined the independent photographers group Le Rectangle. He worked through the Second World War, producing a powerful essay on the removal of Parisian statues by the Germans, who melted them down to make bullets.