Radio journalist Percival Mabasa, 63, was killed by two assailants at the gate of a residential compound in the Las Pinas area of Manila on Monday night, police said.
"That the incident took place in Metro Manila indicates how brazen the perpetrators were, and how authorities have failed to protect journalists as well as ordinary citizens from harm," said the National Union of Journalists of the Philippines.
The national police vowed to bring justice over the attack. The government had no immediate comment.
It followed the fatal stabbing last month of radio journalist Rey Blanco in central Philippines.
The Philippines has one of Asia's most liberal media environments, but it remains of the world's most dangerous places for journalists, particularly in its provinces.
At least 187 have been killed in the past 35 years in the Philippines, according to international watchdog Reporters Without Borders, including 32 killed in a single incident in 2009.
Mabasa's family called his killing a "deplorable crime" and demanded "his cowardly assassins be brought to justice."
Rights group Karapatan described him as "one of the country's fiercest truth-tellers".
Videos on Mabasa's YouTube channel, which has 216,000 subscribers, showed he had been critical of the previous president and some policies and officials in incumbent Ferdinand Marcos Jr's administration.
"We are not discounting the possibility that the shooting could be related to the victim's work in media," local police chief Jaime Santos said in a statement.
(Reporting by Neil Jerome Morales; Editing by Martin Petty)