Bill Dodwell has been appointed tax director for the government's Office of Tax Simplification.
Mr Dodwell will provide expert advice, guidance and direction and has previously served as a non-executive member of the OTS board.
He succeeds Paul Morton, who has held the position since March 2017.
Mr Dodwell is a chartered accountant and chartered tax adviser and was head of tax policy at Deloitte until May 2018, responsible for representations to HM Treasury, HM Revenue & Customs, the OECD and the EU.
He is a former president of the Chartered Institute of Taxation and joined the OTS in July 2018 as a senior policy adviser.
The OTS was established in 2010 to provide advice to the Chancellor of the Exchequer on simplifying the UK tax system and was made a permanent, independent office of HM Treasury in July 2015.
It is currently reviewing the inheritance tax framework over concerns that the system is too complex.
Financial Secretary to the Treasury Mel Stride said: "We are committed to simplifying the tax system and the Office of Tax Simplification is vital in providing informed advice on how to achieve this. Bill Dodwell has the capability and expertise to ensure the OTS continues this valuable work.
"I would like to thank Paul Morton for his exceptional work for the last two years. I am confident he leaves the OTS on a strong footing."
OTS chairman Angela Knight added: "Bill has huge experience and knowledge and is already contributing to the work of the OTS as an advisor. I am delighted to welcome Bill as the new tax director."