HM Revenue & Customs' Phil Pavitt will step down from his role as CIO in January to take up a new role at insurance group Aviva.
Deputy CIO Mark Hall has taken on the CIO role at HMRC, but Pavitt will remain with the department until January to assist with the handover.
Pavitt joined HMRC in 2009, after two years as CIO of Transport for London, and led a transformation project on the department's IT estate leading to claimed savings of £226m.
In an interview with Computing earlier this year, Pavitt said that he had helped cut HMRC's IT costs from 23 per cent of overall running costs to 16 per cent.
He also stated that each year for the next five years, HMRC would save £161m in running costs.
In a statement, HMRC said: "Having completed a number of major transformations at HMRC, Phil indicated that he wished to return to his private sector career. We would like to thank Phil for his work at HMRC."
In the new year, Pavitt will take up the role of global director of IT transformation at Aviva, where he will aim to simplify the insurance company's IT services, and modernise and digitise its business.
He follows a long line of public sector CIOs who have moved to the private sector, including former deputy CIO Bill McCluggage, who is now an advisory technology consultant at storage vendor EMC, and former government CIO Joe Harley, who took up the role of strategic adviser at managed services company Amor Group.
Harley recently told Computing that he was relishing his new role, partly because it isn't hindered by "the big bureaucratic processes" found in government.