Marcos Jr. is the son and namesake of a dictator whose two-decade rule ended in a public revolt and his family's retreat into exile. He is leading by over 30 percentage points and has topped every poll this year. This means Robredo will need a late surge or low turnout if she is to win the presidency.
Polls opened at 6:00 am local time and are set to stay open longer than usual, till 7:00 pm, due to Covid-19 precautions.
Eight other candidates, including former boxing star Manny Pacquiao, Manila Mayor Isko Moreno, and former national police chief Sen. Panfilo Lacson, have lagged far behind in voter preference surveys.
What are the candidates' promising voters?
Both the main candidates have promised to prioritize economic recovery after the pandemic.
Robredo has pledged to increase investment to tackle climate change, level the playing field for business, and promote public-private partnerships.
Marcos, 64, has not presented many details about his policies but is expected to carry ahead with the same approach as his predecessor Duterte, pursuing a ruthless consolidation of power.
Critics say Marcos is attempting to rewrite the family's controversial history for a youthful electorate, though they believe he is unlikely to replicate his father's authoritarian style of ruling.
Duterte's daughter, southern Davao city Mayor Sara Duterte-Caprio, has topped surveys as Marcos Jr.'s vice-presidential running mate.
What's at stake?