Hardie joined the broadcaster four-and-a-half years ago from Procter & Gamble. He resigned yesterday morning and is expected to leave the station in the next few weeks.
Hardie's departure comes at a crucial time for the channel. ITV partners Granada and Carlton Communications have begun to implement plans to overhaul the commercial terrestrial channel and align it with sister brands ONdigital, which is to be renamed ITV Digital, ITV2 and a new sports channel to be launched in August.
Hardie had been credited with turning the channel's marketing strategy round and bringing it up to date. He had even been tipped as a possibility for the new post of ITV managing director, which was taken by Stuart Prebble.
Hardie was also responsible for ITV's first major rebranding in 1999. He introduced an extra weekly episode of Coronation Street and was active in pushing through the rescheduling of the News at Ten.
Prebble said, "He's done a fantastic job for ITV but this really is one of those offers you can't refuse. I wish him every success in the future."