He has asked the Chancellor of the Exchequer to begin the process to appoint his successor.
Randell (pictured) said being chair of both watchdogs had been a “great privilege”.
When he took over the job as chair of the FCA in April 2018 he signed up for a five-year term but is planning to leave his post a year early.
Randell said it was the right time to hand over leadership to a new chair as the regulator prepared to complete its transformation.
“As the FCA prepares to implement its new wholesale, retail and data strategies under an established new executive, now is the right time for a new chair to carry on the close and continuous oversight of our transformation.”
Chancellor of the Exchequer Rishi Sunak, said: “Both organisations undertake a vital role in ensuring that the UK financial markets work well, protecting the interests of consumers, promoting effective competition, and enhancing the integrity of the UK financial system. Charles has led both boards during the UK’s transition to our new position outside the EU, through the vital economic response to the Covid-19 pandemic and supporting the important transition following Nikhil Rathi’s arrival as new chief executive of the FCA.”