The extension will apply to around 2,800 migrant health professionals who are working for the NHS and have UK work visas which are due to expire before October 1.
They will be renewed automatically for a year free of charge so they can remain working in the country, the Home Office said.
The changes will also apply to their family members.
Restrictions have also been lifted on how many hours international student doctors and nurses can work for the NHS per week, according to an announcement on Tuesday.
Deadlines for registered overseas nurses to pass skills tests will also be extended so they have more time to take exams while working on the front line.
NHS migrant health professionals will be able to have their visas extended free of charge.
She added: "We owe them a great deal of gratitude for all that they do.
"I don’t want them distracted by the visa process.
"That is why I have automatically extended their visas – free of charge – for a further year."
The Chancellor of the Duchy of Lancaster told the Downing Street press conference: "More NHS staff are returning to the frontline, and more testing is taking place to help those self-isolating come back, and to protect those working so hard in our hospitals and in social care."
He said a "critical constraint" on the ability to rapidly increase testing capacity is the availability of the chemical reagents, but added the and were working with companies worldwide to ensure the UK gets the material needed to increase tests "of all kind".
Also addressing the presser, NHS England's Medical Director warned it is important the public "must not be complacent" despite a plateau in new cases in recent days.
Stephen Powis said "it's really important not to read too much into this," adding: "It's really important we keep complying with those [lockdown] instructions".
Coronavirus: Everything you need to know