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.
Kearns, a fly-in, fly-out worker and recreational diver, had left Australia in January on vacation with Benson, and attended a friend's wedding in Portugal in recent weeks, according to his mother.
Rui Pereira da Terra, the head of the rescue service in Cascais port near Lisbon, told the news agency Lusa that officials suspected the man and woman had been taking a selfie on a wall above the beach when they fell.
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".
Authorities in Portugal are investigating whether they'd been taking a "selfie" after a mobile phone was found at the bottom of the cliff.
Mr Kearns' parents were notified of their son's death about 1am and were later visited by WA Police.
The British Foreign and Commonwealth Office said: "We are in touch with local authorities following the death of a British woman in Portugal and stand ready to provide support to her family".
Both Australia and the U.K.'s foreign affairs departments said they were coordinating with each other and assisting the families of the vicitms.
The beach is a popular resort with surfers on the south coast of the Algarve.
Pescadores Beach, which translates to Fisherman's Beach, is ringed by cliffs and a wall of up to 40m high.
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.
- Spain manager Julen Lopetegui sacked two days before opening match
- Garmin Adds Music to Vivoactive 3 Smartwatch
- Amelia Kerr registers highest individual score in Women's ODIs
- Jada Pinkett Smith reveals bouts of suicidal thoughts in the past
- Prince Harry and Meghan are coming to New Zealand
- Celtics Made Trade Offer To Spurs For Kawhi Leonard At Deadline
- Martial wants to quit Man United according to his agent
- Peter Navarro's apology to Justin Trudeau for 'hell' remark
- World Cup Returning to US After North American Bid Beats Morocco
- American Red Cross launches 'Missing Types' campaign