Walker was only at the firm for three years until he moved to the United States of America for uncertain reasons. Writing in 1928, Hector Charlesworth suggested that Walker was "chucked down the stairs" and fired for quarrelling with a family relative. However, it is more likely that Walker travelled to Philadelphia for the American Centennial in 1876, an exhibition where Notman and Fraser won the international award, which gave the firm the privilege of exclusive photographic rights for the celebrations. Ultimately, Walker may have decided to stay and pursue painting.