During and after the First World War, the profile of the Leicester Galleries changed and it became known for supporting and promoting modernist art. According to Sir Alec Martin, writing the Foreword of Exhibition,
in 1914 … the firm was beginning to become well known for pioneering contemporary loan exhibitions of modern British art, and one-man exhibitions of both British paintings and the French Impressionists such as Cézanne, Degas, Gauguin, Van Gogh, Matisse, Picasso, Renoir. … They were the first in London and attracted much attention, some abuse and few sales, though the prices asked were very small.
This was also the period in which the gallery began its engagement with sculpture, for which it was to become very well known.
During the First World War, the subject of the war itself became a key theme and the gallery supported the work of British and European artists (many of whom were serving soldiers) who had witnessed the fighting at first hand.