Johnson initially studied medicine but, like Hugh Osmond, only completed the first part of the course, graduating from Oxford University with a BA in Physiological Sciences in 1983.

He began his career as a media analyst at stockbroker Grieveson Grant (subsequently Kleinwort Benson Securities).

An announcement included information that the board had been notified of significant and potentially fraudulent accounting irregularities, that a potential material mis-statement of the company's accounts had significantly impacted the company's cash position, and that Chris Marsh, the chief financial officer, had been suspended from his role.

[6] On 22 January 2019, the firm announced that it had collapsed into administration following failed talks with banks, which the company stated was a "direct result of the significant fraud".

Risk Capital Partner's portfolio includes the directory publisher Superbrands, fashion chain East,[8] and GRA, the UK's largest greyhound track owner.

Through Risk Capital Partners, Johnson was a founder, part-owner and director of recruitment business InterQuest Group plc.

After being confronted during filming about low wages, Johnson stormed off the show, unwilling to listen to or act on criticism from employees about poor working conditions.

Johnson also purchased in 2010 a stake in artisan bakery Flour Power City, which supplies restaurants, hotels, and caterers.

September 2010 saw Johnson purchase Feng Sushi,[25] a London-based chain of Japanese restaurants specialising in home delivery.

In May 2015, Risk Capital Partners announced its purchase of a majority stake in Zoggs, the global swimming products brand.

[31] Among Johnson's business maxims are that, consciously or not, every successful company that he knows has followed kaizen, the Japanese management philosophy of constant, incremental improvements, often driven from the bottom up.

[32] Johnson supported Brexit and backed the Vote Leave campaign group in the 2016 United Kingdom European Union membership referendum.

[33] Johnson has described the government's response to COVID-19 as "a campaign of fear"[34] and in November 2020 Risk Capital Partners funded a media consultant for the COVID Recovery Group of anti-lockdown MPs.

[40] In June 2012, Johnson was appointed chairman of Startup Britain, the national campaign to stimulate start-up growth in the UK.

[42] In October 2013, Johnson co-founded and launched the Centre for Entrepreneurs,[43] a non-profit think-tank aiming to address the "...under-representation of entrepreneurs in the public eye" and to "...promote entrepreneurship to government, media, the private sector (including big businesses) and the general public.

With Stephen Lambert and Christopher Hird, Johnson co-produced The Flaw,[45][46] a 2011 documentary film detailing the events leading up to the financial crash of 2008.

The film takes its title from Alan Greenspan's admission to US Congress that he had been mistaken to put so much faith in the self-correcting power of free markets.