David Cameron, 57, served as British prime minister from 2010 to 2016, resigning after the outcome of the Brexit referendum, when Britain voted to leave the European Union.
His unexpected return to the front line of British politics comes after he spent the last seven years writing his memoirs and involving himself in business, including Greensill Capital, a finance firm which later collapsed.
Greensill's demise fuelled questions about the extent to which former leaders can use their status to influence government policy after Cameron repeatedly contacted senior ministers in 2020 to lobby for the firm.
Sunak's office said on Monday that King Charles had approved giving Cameron a seat in Britain's upper chamber, the House of Lords, allowing him to return to government as a minister despite no longer being an elected member of parliament.
Meanwhile, under fire from opposition MPs and members of the governing Conservative Party to eject interior minister Suella Braverman, Sunak seemed to have brought forward the long-planned reshuffle.
Sunak was forced to sack the interior minister when the ever-controversial Braverman defied him last week in an unauthorised article accusing police of "double standards" at protests, suggesting they were tough on right-wing demonstrators, but easy on pro-Palestinian marchers.
The opposition Labour Party said that inflamed tensions between a pro-Palestinian demonstration and a far-right counter protest on Saturday, when nearly 150 people were arrested.
Braverman was replaced by James Cleverly, who had relished his job as foreign minister but who is seen as a safe pair of hands.
But Braverman's removal and Cameron's return angered some Conservatives on the right of the party. One MP said her removal was disappointing and Braverman could become a vocal force on the backbenches in parliament.
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