Mr Johnson lauded GB News, which has been the target of an advertising boycott because of the Right-wing views expressed by many of its presenters, as a “remarkable new TV channel”.
He went on to promise viewers his “unvarnished views” on subjects including the influence of China on the world stage and Russia’s invasion of Ukraine.
GB News said Mr Johnson, who was born in New York, would play a key role in its coverage of both the UK and US general elections next year.
He will also devise and present a new series which the channel said would “[showcase] the power of Britain around the world”, in addition to presenting “occasional” live television programmes across the country.
A letter from the anti-corruption watchdog Acoba published by the Daily Mirror showed that Mr Johnson had sought permission for his new broadcasting gig, a requirement on former ministers whenever they enter a new job.
He had previously been rebuked by Acoba after giving it only 30 minutes’ notice of his new role as a Daily Mail columnist.
Figures published in December 2022, while Mr Johnson was still a Tory MP, showed he had made more than £1 million by delivering four speeches within the space of just six weeks.
Mr Johnson stood down as an MP on June 10 as he accused the privileges committee of being determined to find him guilty of deliberately misleading Parliament over the partygate scandal. The committee was expected to recommend a suspension of more than 10 days.
The Conservatives narrowly won the by-election that took place the following month in his old seat of Uxbridge and South Ruislip, which he had represented since 2015.
Mr Johnson is the latest politician to sign to the network, which counts among its presenters Conservative MPs Philip Davies and Esther McVey, who are married and host a joint programme together, and Lee Anderson, the deputy Tory chairman.
Nigel Farage, the former Ukip leader, also has his own slot, while other GB News presenters include the veteran broadcasters Eamonn Holmes and Anne Diamond.
Last month, GB News suspended three presenters amid a backlash to misogynistic comments made on the channel. It has since confirmed that Laurence Fox, the former actor, and the Rev Calvin Robinson, a deacon in the Free Church of England, will not be returning to the broadcaster.
Dan Wootton, a former show business journalist, remains suspended while an internal investigation is carried out into allegations of impropriety against him, which he denies.