The man, who was in his 40s, and the woman in her 30s were apparently taking a picture on top of a wall that overlooks Pescadores beach in Ericeira when they plunged to their deaths between 1 a.m. and 6 a.m.
It is not the first time tourists have fallen off the wall.
Mr Kearns was a FIFO worker on Chevron's Wheatstone project in the Pilbara, and they were both keen divers, particularly Ms Benson.
The Department of Foreign Affairs and Trade confirmed it is providing consular assistance to the family and is in contact with the British Foreign and Commonwealth Office.
Cops have sealed off the beach while investigations continue into exactly what happened.
The bodies of the British and Australian tourists were found on a beach in Ericeira with their phones and other possessions nearby, reports The Guardian.
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'Everything seems to indicate that the fall happened when they were probably trying to take a selfie, ' said Rui Pereira da Terra, head of the rescue service in Cascais port.
"Since we found a mobile phone on the wall, everything suggests the victims might have been taking a selfie, when they allowed the phone to fall, leaned over to grab it and fell".
Praia dos Pescadores, or Fishermans Beach, is surrounded by cliffs and a 40-metre high wall.
The spokesperson did not confirm the nature of the incident or say how the woman died. "Owing to our privacy obligations we will not provide further comment", a DFAT spokesperson said. Picture: SuppliedThe large stone wall sits 30m above the popular surf beach.
The couple's bodies were taken to a medical centre while authorities contacted the Australian and British embassies in Lisbon.