The girl - believed to be around two-years-old - was found crying in a buggy by passers-by during a family holiday in Carcavelos, a village around 15 miles west of Lisbon.
The Daily Mail reports her parents - who were described by local newspaper Diario de Noticias, as 'middle-class teachers' - were found around 100 yards away, so drunk they could not confirm their daughter's name.
The Public Security Police (PSP) released a statement saying: "The PSP were called to an incident in Carcavelos where a child was in a baby buggy having been abandoned.
"It was possible to identify the parents about 100 meters away, in an advanced state of drunkenness. The PSP were able to feed the child soup and water, and later at the police station, with fish and cooked vegetables.
"Given the dangerous situation the child was in, she spent the night at the Emergency Reception Centre for Minors in Carcavelos.
Fabio Castro, PSP spokesman then added: "The girl's parents were about 100 metres away, sat on an esplanade, completely drunk.
"They weren't able to confirm if they were the child's parents because they refused to obey the police's orders. The officers tried to communicate with them in several languages."
A court is now deciding when the little girl will be returned to her parents.