Police said the mother was found by authorities showing signs of having been restrained and assaulted.
She was taken to a nearby hospital to be treated for her injuries, police added.
“The alleged perpetrator had already served a prison sentence for aggravated homicide, and the family had been flagged following domestic violence cases registered in 2022 and 2023,” a spokesperson said.
Portuguese TV news channel SIC NotÃcias reported that the mother and child are British.
However, it is reported the suspect was a Portuguese citizen.
The Criminal Investigation Department of Leiria is leading the investigation into the two deaths.