The man and woman reportedly lost their balance while taking photographs of themselves overlooking the coastal town of Ericeria, 30 kilometres from Lisbon, where they fell roughly 30 metres to their death, according to local media.
It's understood the couple may have been taking selfies after a phone was found at the bottom of the cliff.
Local media reported the pair were both Australian, however, the Department of Foreign Affairs and Trade said one Australian had died, and the department had been in contact with its British counterpart over the second death.
A local naval official in the area says authorities believe the couple fell off the 90-foot wall while they were attempting to take a selfie.
Kathy Kearns posted on Facebook: "It is with a heavy heart I have to announce that Michael and Louise were taken from us in a tragic accident in Portugal".
He reportedly said to the Lusa news agency that "since we found a mobile phone on the wall, everything suggests the victims might have been taking a selfie".
The report did not name the couple but said the woman was 30 and the man 40, although other reports gave slightly different ages.
Mr Kearns was a fly-in fly-out (FIFO) worker at Chevron's Wheatstone project in the Pilbara, Western Australia, and enjoyed diving.
Mr Kearns' mother told PerthNow the couple, who lived in Perth, had been holidaying overseas since January, and had been in Portugal for a friend's wedding.
"Owing to our privacy obligations we will not provide further comment".
Ericeira is a fishing town that's popular with surfers and tourists alike. According to AFP it's not the first time tourists have fallen from the wall situated near the Praira dos Pescadores beach.
It is a popular hotpot, with countless tourists uploading their pictures of the enormous wall on Instagram.