Boris Johnson told the cabinet they had “a momentous task ahead”, as he repeated his commitment for the UK to leave the EU on 31 October.
On Wednesday, Mr Johnson gave key roles to leading Brexiteers.
The appointments saw Sajid Javid as chancellor, and Dominic Raab and Priti Patel return to government.
Mr Raab was made foreign secretary and Ms Patel is home secretary.
More than half of Theresa May’s old cabinet, including leadership rival Jeremy Hunt, quit or were sacked.