Mr Farrant has been appointed chief executive of Leisure Connection, the UK's largest management company for public sector sports and leisure.
Mr Farrant has worked at the council for the past four-and-a-half years, and in local government for 26 years. He was a judge in last year's LGC Awards.
During his tenure, the council achieved beacon status for transforming secondary education. It also won several awards for management, social services and private finance initiatives.
Mr Farrant leaves the council on 7 November and begins his new post the following day.