The announcement came one year after the world's biggest social network gained observer status at GNI, whose corporate members include Microsoft, Yahoo! and Google.
"We welcome Facebook as a full member of GNI and look forward to working more closely with them to advance the freedom of expression and privacy rights of Internet users worldwide," said the group's executive director Susan Morgan.
"Adding the power of Facebook's community of one billion global users puts GNI in an even better place to press governments to fulfill their obligations to protect rights online."
"We're pleased to join GNI and contribute to its efforts to shed a spotlight on government practices that threaten the economic, social and political benefits the Internet provides."
Other GNI members include the Center for Democracy and Technology, Committee to Protect Journalists, Electronic Frontier Foundation and Human Rights Watch.