The 45-year-old was dragged from the sea by surfers about 2.30pm on Thursday after he went in to help his two daughters, aged 9 and 12.
A nurse, who happened to be sunbathing on the unsupervised Praia da Calada in Mafra, spent 50 minutes trying to revive to no avail.
The girls suffered minor injuries and were taken to a hospital in Lisbon with their mother.
The father worked in Dubai on a British passport, local reports said.
The beach has no lifeguards until June 12 and no mobile reception creating logistical problems for paramedics.
Commander Paulo Agostinho, from the Captaincy of Cascais, asked holidaymakers to “avoid going to beaches without surveillance at all”.
“Drowning kills in seconds and on unguarded beaches there are no permanent means of rescue,” he explained.
“At Calada beach there isn’t even a GSM network [mobile phones] and it was necessary to use radios”.
Praia da Calada is a long sandy beach. The popular surfers’ spot is surrounded by tall cliffs which protect it from strong winds.