Ms Mahmood, considered a "blue Labour" social conservative, will take charge of the police, MI5 and the government's domestic direction of travel at a time of great flux.
Sir Keir Starmer is reshuffling his cabinet following Angela Rayner's resignation after admitting she had not paid enough stamp duty on the purchase of a new home.
Angela Rayner referred herself to the independent adviser on ministerial standards - who concluded she had breached the ministerial code. This is the adviser's full verdict.