Risk boss Nathan Bostock will replace him as finance head from October.
The bank plans to float between 20 and 25 per cent of Citizens over the next two years with an IPO in New York.
It is part of a wider move by the state-backed lender to cut down overseas operations to focus on UK retail banking services. And the sale should also free up valuable capital for the bank, helping bring the group back to health.
Meanwhile investor group the Local Authority Pension Fund Forum urged its 56 member funds to vote against RBS’ accounts at the AGM next week.
It argues there is a black hole of up to £10bn of likely future losses in the bank’s accounts, as rules make RBS report incurred losses, not expected losses.
“RBS is fully compliant with international accounting standards and has market leading financial disclosures,” said a spokesperson for the bank.