"Hello, Facebook! I finally got my very own page," Obama said, nearly six months after joining Twitter.
"I hope you'll think of this as a place where we can have real conversations about the most important issues facing our country - a place where you can hear directly from me, and share your own thoughts and stories. (You can expect some just-for-fun stuff, too.)," he said.
"Not only do I want future presidents to be able to take walks like this," Obama said ahead of the Paris Climate Summit where the US has said it would push for an ambitious climate change agreement.
"I want to make sure that the American people are able to enjoy the incredible national parks, incredible beauty, the mountains, the oceans, that have been one of the greatest gifts we've ever received."
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Facebook founder Mark Zuckerberg soon welcomed Obama on the popular social networking site.
"Welcome, President Obama! I'm excited that you've joined our community, and I look forward to seeing how you engage with people here on Facebook," Zuckerberg said.
The "Barack Obama" Facebook account, which has over 45 million followers, continues to be run by Organizing for Action.
Obama has been more active on social media as his second innings in White House nears its end, CNN reported.