They were said to have fallen between 1am and 6am.
The couple are believed to be from Britain and Australia.
Reports said two Australians may have been taking selfies when they fell about 30 metres in the town of Ericeira.
Mr Kearns was a fly-in, fly-out worker on Chevron's Wheatstone project in the Pilbara and was a keen recreational diver in his spare time.
"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", he was quoted as saying.
Australian Michael Kearns, 33, and his British girlfriend Louise Benson, 37, were standing on a wall overlooking the picturesque Praia dos Pescadores beach in Ericeira early Tuesday, when their phone slipped, Perth Now reported. Picture: GettyMs Benson posted this image to social media showing the cliff in the background.
A spokesperson for the Foreign Office said: "We are in touch with local authorities following the death of a British woman in Portugal and are providing support to her family".
The woman from the United Kingdom who died is reported to have been 30.
Both Australia and the U.K.'s foreign affairs departments said they were coordinating with each other and assisting the families of the vicitms.
Ericeria is a fishing and surfing town on Portugal's western Atlantic Ocean coast, 50km north-west of capital Lisbon.
It is a popular hotpot, with countless tourists uploading their pictures of the enormous wall on Instagram.
Their bodies were taken to a medical centre while Portuguese authorities alerted British and Australian embassies in Lisbon.
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