Mr Javid, a former chancellor and home secretary, was announced as Mr Hancock’s replacement by Downing Street last night.
His return to cabinet comes just 16 months after he quit as chancellor in a row with the prime minister who had ordered him to sack his aides.
Making his first statement as health secretary today (June 27), he thanked Mr Hancock and vowed to get on with ending the pandemic.
Police shut Buxton road after diggers report bomb discovery
14 photos show parched fields, dwindling rivers and barren reservoirs across Derbyshire – as drought is officially declared
Buxton mum and daughter donate hair to Little Princess Trust cancer charity
Shocking CCTV footage shows moment man smashes glass into another man's face in Buxton pub
High Peak MP seeks bus service guarantees amid Greater Manchester shake-up
He said: “Matt Hancock worked incredibly hard, he achieved a lot and I’m sure he will have more to offer in public life.
“I was honoured to take up this position. I also know that it comes with huge responsibility, and I will do everything I can to make sure that I deliver for the people of this great country.
"We are still in a pandemic and I want to see that come to an end as soon as possible, and that will be my most immediate priority to see that we can return to normal as soon and as quickly as possible.
“Now I’ve got a lot of work to do and I’m sure you appreciate that, and if you can excuse me I’d like to get on with it.”
Mr Hancock announced his resignation on Saturday after pictures and video emerged of him and colleague Gina Coladangelo – who are both married with three children – kissing.
In a letter to the prime minister, he said: “The last thing I would want is for my private life to distract attention from the single-minded focus that is leading us out of this crisis.”
A statement from No 10 released around 90 minutes later said: “The Queen has been pleased to approve the appointment of the Rt Hon Sajid Javid MP as Secretary of State for Health and Social Care.”
Mr Javid said: “I look forward to contributing to our fight against the pandemic, and serving my country from the Cabinet once again.”
It is understood that Mr Hancock has ended his 15-year marriage to his wife, Martha.
Friends of the former health secretary say his relationship with Ms Coladangelo is "recent but serious", Sky News reports.