According to Sky News, Thomson, who stepped down as Metro Bank chairman in 2012, has secured First Direct chief executive Mark Mullen to lead the new venture.
It is understood the new business will launch in 2015, subject to regulatory approval. It will not have any physical branches and its services will be run online and through apps.
Both former marketers, Thomson co-founded Metro Bank in 2008, while Mullen, who is the chief executive of First Direct, was formerly the head of marketing at the HSBC-owned bank.
Designed entirely for the digital age, Atom will be the
UK’s first real alternative to the established banks
Thomson said: "Designed entirely for the digital age and with none of the legacy issues of the past, Atom will be the
"Atom will be led and governed by an experienced and imaginative team who have a passion for people and know what it takes to put the customer at the heart of an organisation. Together we will offer our personal and business customers both better customer service and better value.
"We believe that Atom will be the 21st century choice for customers who want a bank that’s not just different, but more importantly, better."
In 2009, Mullen left his position at the bank to take on a senior marketing role at HSBC Bank Middle East. He returned to the bank as chief executive in 2011.
Writing for Marketing last year, Thomson said ahead of the TSB and Tesco brands' entrance into the retail banking sector, that marketers must put the needs of their customers before the needs of the bank.