No official reason has been given for the split, but insiders attribute it to creative differences and issues over agency remuneration.
Sony appointed Fallon to work on its Walkman brand and the online music service, Connect. The electronics giant overhauled its roster in June this year after dropping Young & Rubicam New York. It also hired McKinney & Silver to work with Sony's long-time small agency partner, Bagby & Co.
Fallon continues to work with Sony in Japan and Europe.