Sharpe, who joined the business in 1972, told PRWeek that he agreed redundancy terms with the bookmaker after being informed he was "at risk" of redundancy.
He said: "At no time during my employment with the company have I ever expressed a wish to leave."
Sharpe said he would continue working on a freelance basis for the bookmaker, organising and promoting its Sports Book of the Year prize.
William Hills comms director Ciaran O'Brien said Sharpe's 45-year career was a "remarkable testament to his talent and stamina".
His departure follows that of public relations manager Jon Ivan-Duke, who left the business last month. Ivan-Duke had been with William Hill since 2013, following several years as a radio broadcaster, his LinkedIn profile says.
Sharpe and Ivan-Duke will not be replaced, although O'Brien did confirm that Tony Kenny, who is head of sponsorship PR at William Hill, will now sit in the PR team rather than the marketing team.