Gavin Williamson has been removed as education secretary and Robert Buckland has been removed as justice secretary in the first big moves of the cabinet reshuffle.
The full shuffle is expected to be announced over the next two days.
Westminster has been anticipating that the prime minister will attempt a reshuffle for several weeks.
A Downing Street source said: “The prime minister will today conduct a reshuffle to put in place a strong and united team to build back better from the pandemic.”
Meanwhile, Boris Johnson has refused to explain how universal credit claimants would be able to recoup their looming £20-a-week cut in payments.
The prime minister was challenged to set out how many hours of extra work will be needed – after a Cabinet minister wrongly claimed it is just two.
But Mr Johnson declined to say whether the true figure is higher or lower.
