Mr Sunak is facing calls for an official inquiry into Ms Braverman after he reappointed the home secretary six days after she was sacked by departed PM Liz Truss for a security breach.
Labour leader Sir Keir used his first questions to quiz Mr Sunak on why he had made the reappointment.
Taking his first Prime Minister’s Questions, Mr Sunak defended the re-appointment, saying Ms Braverman had accepted making an “error of judgment”.
"The home secretary made an error of judgment, but she recognised that, she raised the matter and she accepted her mistake, and that’s why I was delighted to welcome her back into a united Cabinet that brings experience and stability to the heart of government,” Mr Sunak said.
"And let me tell you, Mr Speaker, what the home secretary will be focused on. She’ll be focused on cracking down on criminals, on defending our borders, while the party opposite remains soft on crime and in favour of unlimited immigration.”
Sir Keir responded: “Yesterday the Prime Minister stood on the steps of Downing street and promised integrity, professionalism and accountability, but then with his first act, he appointed a home secretary who was sacked by his predecessor a week ago for deliberately pinging around sensitive Home Office documents from her personal account.”
The Labour leader added: “We can all see what’s happened here. He’s so weak he’s done a grubby deal, threatening national security because he was scared to lose another leadership election. There’s a new Tory at the top, but as always with them, it’s party first, country second.”
It comes as Downing Street confirmed Chancellor Jeremy Hunt’s planned Halloween budget to get the public finances back on track had been delayed until next month.
The medium term fiscal plan will now be published on November 17 as an autumn statement, alongside a new set of economic forecasts from the Office for Budget Responsibility.