Bostock was said to be considering a position as chief risk officer at Santander UK.
RBS confirmed speculation over Bostock’s future after a board meeting when the topic was said to have been discussed.
In a statement, RBS said: “Royal Bank of Scotland Group can confirm that Nathan Bostock has this evening informed the board of his intention to resign from his role as group finance director. His formal resignation is expected soon, but he will remain in his position to oversee an orderly handover of his responsibilities.
“Details on arrangements for his successor will be announced in due course.”
It will be a fresh blow for group chief executive Ross McEwan, reeling from a number of setbacks in the past week. RBS was handed a heavy fine for its role in rigging a benchmark interest rate, suffered another IT meltdown and faced a legal challenge from a group of investors.
Bostock took up his present role from Bruce Van Saun who left to run RBS’s Citizens Bank in the US.