Once inside the cathedral, Johnson read from Philippians 4:8, which states: “Whatever is true, whatever is honorable, whatever is just, whatever is pure, whatever is pleasing, whatever is commendable … think about these things.”
More than 400 people attended the service, including former prime ministers David Cameron and Tony Blair, the Times UK reported.
Queen Elizabeth, 96, skipped the service due to health issues after reportedly experiencing “some discomfort” after attending events on Thursday.
In a Times interview last July, Johnson hailed Christianity as “a superb ethical system” but added that he would count himself “as a kind of very, very bad Christian.”
When asked to respond to reports that a friend described the prime minister as holding to a “pre-Christian morality system with a multitude of gods and no clear set of rules,” Johnson replied: “Christianity is a superb ethical system and I would count myself as a kind of very, very bad Christian.
“No disrespect to any other religions, but Christianity makes a lot of sense to me.”
When he was asked at last year’s G7 summit whether he was a practicing Catholic, Johnson initially balked at a response.
But after being told that Labour Party leader Keir Starmer said the prime minister did not believe in God, Johnson promptly quoted Psalm 14:1, which says, “The fool has said there is no God.”
Johnson — who was baptized a Catholic but was twice married as an Anglican before his third marriage to Carrie Symonds — also took part in a Bible reading project for the King James Bible Trust in 2011.
The prime minister read from Isaiah 11. He called the King James version the “single most beautiful and influential work of English literature.”