Carlito Lana, 37, was executed in Riyadh on Friday for shooting a Saudi national before running him over with a car, the Saudi Press Agency reported.
Migrante International, an advocacy group for the millions of Filipinos working overseas, condemned the execution, saying the government of President Benigno Aquino had failed to adequately defend Lana.
"This shows migrant rights are not protected. There is not enough legal assistance given by the Aquino government to our expatriates abroad," said Mic Catuira, spokesman of the group.
"That is why our Filipinos abroad go through these travesties," he said, insisting that Lana had acted in self defence when he killed the Saudi man in December 2010.
The foreign department said it hired law offices and provided Lana with all necessary assistance during the trial to ensure his rights were respected.
"Mr. Lana was given a fair trial," it stressed in a statement.
The family of the slain man refused to accept "blood money", or a cash payment in exchange for forgiving Lana and sparing him from execution, it said.
According to Migrante International, six Filipinos have been executed abroad since 2010.
Catuira conceded that Lana’s execution took his group by surprise.
Foreign Department spokesman Charles Jose likewise said that the government was not aware that Lana was due to be executed Friday.
About 10 per cent of Filipinos work overseas, attracted by the higher salaries than they can earn at home. Their remittances are a major pillar supporting the country’s economy.
The welfare of Filipino overseas workers is a volatile issue at home and Manila has in the past lobbied foreign governments, including Saudi Arabia and China, to save the lives of Filipinos on death row in those countries.