'I'll sleep better at night,' says actor
He said that he had made decision because Facebook boss Mark Zuckerberg "values profit more than truthfulness".
The actor linked to a story about Facebook's decision to allow political ads that include lies or falsehoods, which has attracted criticism from those who argue the site is enabling misinformation.
The company says that such decisions should be made by regulators rather than private companies.
But Hamill suggested Facebook was looking for the money that comes from political advertising.
"So disappointed that #MarkZuckerberg values profit more than truthfulness that I've decided to delete my Facebook account," he wrote on Twitter. "I know this is a big 'Who Cares?' for the world at large, but I'll sleep better at night. #PatriotismOverProfits"
Facebook did not comment on Hammill's departure or his post. It pointed to new policies, published last week, which it says will allow people to see fewer ads about political or social issues.
"We recognise this is an issue that has provoked much public discussion — including much criticism of Facebook’s position," wrote Rob Leathern, Facebook's director of product management. "We are not deaf to that and will continue to work with regulators and policy makers in our ongoing efforts to help protect elections.
"We are grateful to everyone who has engaged with us over the past several months. With these changes, we believe we offer unprecedented transparency and control for political ads, and look forward to continuing the discussions and updates over the next year."