Christian Wakeford crossed the floor in protest at the PM’s leadership and the row over Downing Street parties.
He has also said he was threatened about the loss of a school in his constituency if he did not toe the line.
Writing in the Sunday Mirror, Mr Wakeford said: “Boris Johnson is living on borrowed time. He has poisoned the Tory Party from top to bottom.”
The Bury South MP said the investigation into No 10 by civil servant Sue Gray would show Downing Street was “hosting parties while the rest of us were obeying the rules”.
“The PM attended and then lied about it. He showed no respect for the Queen while she was in mourning for her husband,” Mr Wakeford wrote.
“His behaviour has been an insult not just to Her Majesty but to the whole nation.
“His lack of honesty and integrity has poisoned the once great party he leads.”
Mr Wakeford added he had “too much respect for the people who voted me into Parliament to stay silent in the face of such intimidation”.
It comes amid calls for another inquiry after a Tory MP said she was told that she was sacked from her ministerial post because her Muslim faith was “making colleagues uncomfortable”.
Nusrat Ghani said when she lost her job as a transport minister in 2020, a Government whip told her “Muslimness” had been raised as an issue at a Downing Street meeting to discuss the reshuffle.