"This acquisition will allow us to scale the business and ensure we can introduce as many people as possible to a new way of banking."
Under the terms of the agreement, Tandem will acquire 100% of Harrods Bank and benefit from around £80m of capital coming into the business.
The financial terms have not been disclosed but subject to regulatory approval, the bank will operate under the Tandem brand.
The acquisition will accelerate Tandem’s launch plans to offer savings accounts to its customers before the end of the year.
Tandem’s money management app is already available and credit cards are set for launch in the next few months.
Ricky Knox, Tandem founder, said: “Tandem has been built from the ground-up with the help of over 11,000 co-founders, who have helped us shape products and services that really make a difference to their lives. This acquisition will allow us to scale the business and ensure we can introduce as many people as possible to a new way of banking.”