After briefly attending Roehampton Technical Institute to study shipping management, Walker worked in advertising for Dunlop and Aspro. He was then headhunted by McCann Erickson, where he worked on the firm's account with Esso. Following this, he was employed as an accounts director by the Masius advertising agency, with clients including British Rail, Vauxhall and Mars, for whom they created the slogan "A Mars a day helps you work rest and play"; Walker repeatedly denied the attribution of the slogan to himself, saying that he was only an administrator on the project. He did not retire from this until the age of 59, long after he had gained fame as a commentator. He also briefly competed in motorcycle races himself.