The Conservative former prime minister was the fifteenth MP on Wednesday to take an oath of allegiance to Charles.
Mr Johnson frolicked within the queue chatting with DUP MP Sammy Wilson (East Antrim) and Transport Secretary Anne-Marie Trevelyan.
Holding the King James Bible, Mr Johnson stated: “I swear by almighty God that I will likely be devoted and bear true allegiance to His Majesty King Charles, his heirs and successors, in keeping with regulation, so assist me God.”
Ms Trevelyan was the primary MP to swear in on Wednesday adopted by Dwelling Secretary Suella Braverman.
MPs are sworn in after every normal election to allow them to take their seat, converse in debates, vote and obtain a wage.
The wording of the oath means MPs have already pledged their allegiance to the heirs and successors of the Queen, that means they don’t have to do it once more at this level.
A complete of 31 MPs pledged their allegiance to Charles through the first swearing-in session.
Commons Speaker Sir Lindsay Hoyle opened proceedings by thanking parliamentary employees, members of the armed forces and others for his or her efforts through the Queen’s lying-in-state and funeral.
He advised MPs: “I additionally wish to placed on report my gratitude to all those that helped guarantee occasions of the final 10 days or so have been managed with such dignity and brilliance, albeit within the saddest of circumstances.
“That features, after all, many outdoors this Home, together with our armed companies, the police and numerous others.
“I wish to say a really particular thanks particularly to all these parliamentary employees, together with colleagues who volunteered to tackle roles past their day jobs who contributed and also you ensured that Parliament was capable of play its half safely, respectfully and with delight, and so I’m extraordinarily grateful for all that has been performed.”
MPs can swear the oath or affirm all through Wednesday, with Sir Lindsay additionally advising: “I remind members that swearing-in is recorded by the tv cameras, something stated or performed by members could seem on tv or could also be picked up on the microphones.”
Regular enterprise within the Commons will resume on Thursday.