EGS, which has worked on the account since October 2007, will continue to be the bookmaker's planning specialists, working with The7Stars.
The company's £5m internet account will continue to be handled by i-level.
William Hill was established in 1934 and became the biggest betting shop in the UK in 2005, following the acquisition of 624 Stanley Leisure offices for £504m.
According to The Nielsen Company, William Hill spent £10.2m in the 12 months to 30 November 2008, with the bulk of its activity (£4.9m) being directed online followed by £3m for press.
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