Transport secretary Grant Shapps confirmed the move in a tweet shortly after 5pm on Thursday (20 August).
It means those returning to the UK from Portugal will no longer have to self-isolate for 14 days.
Croatia, Austria and Trinidad & Tobago, meanwhile, have had their travel corridors revoked.
"Data shows we can now add Portugal to those countries included in travel corridors," said Shapps.
"As with all air bridge countries, please be aware that things can change quickly. Only travel if you are content to unexpectedly 14-day quarantine if required."
Portugal’s travel corridor will come into effect from 4am on Saturday (22 August), the Department for Transport has confirmed.
It has also been exempted from the Foreign Office’s global advisory against all but essential travel.
Previously, only the country’s Madeira and Azores archipelagos has been exempt.
"Portugal has been added to the government’s travel corridor list following a decrease in confirmed cases of coronavirus," said the DfT in a statement.
"Passengers arriving in England from Portugal at or after 4am on Saturday 22 August will not need to self-isolate, so long as they haven’t been in or transited through any other non-exempt countries in the 14 days preceding their arrival.
At the same time, the Foreign and Commonwealth Office (FCO) has updated its travel advice... Portugal has been added to the list of destinations that are exempted from the FCO’s global advisory against non-essential travel."
Portugal has been conspicuous by its absence from the UK’s travel corridor list, owing to its consistently low rate of coronavirus infection.
The country has also enacted a number of tourism-specific schemes to ensure its tourism sector is Covid-secure, including a Clean & Safe certification scheme.
More than 20,000 tourism businesses have been awarded the stamp.
Reacting to the decision, Advantage Travel Partnership chief executive Julia Lo Bue-Said said: “To have such a popular destination like Portugal added to the ‘safe list’ of travel corridors is of course positive news for British travellers and the wider industry."
