The move will be completed once a successor has been appointed “and a smooth transition of responsibilities has taken place”, the lender said.
The board explained the search for a new CEO will commence shortly.
Chairman John Callender said the board wanted to thank Pateman (pictured) for his contribution to the business since becoming chief executive in January 2016.
“The bank has made significant progress under his leadership and now has the right foundations to move forward into the next phase of its evolution,” he said.
“Given the change in ownership last year, Steve and the board felt it important that the bank’s leadership shared the time horizons of the investment case and will now work together to secure a successor who can lead the bank through that phase.”
Pateman added: “It has been a privilege to lead Shawbrook through some challenging times and the progress we have made in financial metrics and organisational structure will lay the foundations for future growth and opportunity.
“It has been a great experience and one that I am sure will serve me well in the future.”