The Labour politician’s identity was revealed after he failed to impress the panel of judges with his rendition of Walk Like An Egyptian by The Bangles, and progress through to the next round.
Johnson, who has often spoken of his ambition to be a pop star when he was a teenager in the 1960s, served in both Tony Blair and Gordon Brown’s governments and was last in the cabinet in 2010.
He stood down from frontline politics at the 2017 general election.
The ITV programme, which debuted on Saturday and continued on Sunday night, sees celebrities and public figures compete dressed in elaborate outfits which conceal their identity.
A prominent politician appearing on a prime-time entertainment show is not unique. But seeing a former minister of state take off an elaborate Egyptian-inspired outfit, and coming hard on the heels of the Brexit fall-out, another general election and with the Labour leadership contest just days away, was too much for some.
And Rita Ora’s reaction was something to behold.
Speaking after he was unmasked by host Joel Dommett, Johnson said: “It was brilliant. What a show. In the mask you feel like a bit of a spaceman. You are removed from it all.
“I couldn’t really see the dancers dancing around me. It was so much fun. A bit of karaoke as well.”
The judging panel of Jonathan Ross, Davina McCall, Ken Jeong and Rita Ora failed to guess his identity despite a number of clues.
“I saw the queen everyday” pointed towards his former job as a postman, and “my place of work is also a piece of furniture” hinted towards his governmental role in the cabinet.
Before he was unmasked, Ross suggested Pharoah might be Brexit Party politician Ann Widdecombe, who has appeared on Strictly Come Dancing.
And at one point Ross even mentioned Johnson’s name, before conversation swiftly moved on.
It comes after the debut episode of the surreal celebrity guessing game won Saturday night’s ratings battle against BBC One’s The Greatest Dancer, pulling in over two million more viewers.
The Masked Singer kicked off with an average audience of 5.5 million when it aired at 7pm, according to overnight ratings.
The Greatest Dancer, which also aired at 7pm, had an average of 3.2 million viewers.