In a video message on his Twitter feed, the health secretary said his symptoms were “very mild” and he was self-isolating at home with his family.
His initial positive test was provided by a quick-turnaround lateral flow test, and he is now awaiting confirmation from a PCR test, which is considered more reliable.
Mr Javid, 51, said: “This morning I tested positive for Covid. I’m waiting for my PCR result, but thankfully I’ve had my jabs and symptoms are mild.
“Please make sure you come forward for your vaccine if you haven’t already.”
Mr Javid said he took the test on Friday night after feeling “a bit upset”.
“I am now self-isolating at home with my family till I get the result of the PCR test,” he said.
“I’m grateful that I’ve had the vaccine twice, and so far my symptoms are very mild.”
He urged anyone who has not yet been offered vaccines to “get out there and get them as soon as possible”.
And he continued: “If, like me, you may feel a little nervous, or you think have come into contact with someone who is positive, please take a lateral flow test as well.
“If everyone plays their part, you are not only protecting yourself and your loved ones, but you are also protecting the NHS and helping to preserve our way of life.”
Mr Javid is the latest in a string of senior government ministers and officials who have been hit by Covid-19, including his predecessor Health Secretary Matt Hancock and Prime Minister Boris Johnson, who spent three days in intensive care last year.
He appeared in the chamber of the House of Commons on Wednesday to start a debate on the health and social care bill, although it is not clear whether he was infected at the time.
It is not yet known whether he met Prime Minister Boris Johnson face-to-face in the past few days as the cabinet was held virtually on Tuesday.
A positive PCR test will trigger an effort by NHS Test and Trace to identify contacts who may have been infected.
Ministers, officials and Whitehall staff now face the prospect of being called or “pinged” by a smartphone app in the coming days should they, too, go into self-isolation.