"Our company is on a critical journey". Clegg will take over from Elliot Schrage and will report to the Sheryl Sandberg, the firm's chief operating officer. Mr Clegg lost his own seat in Britain's parliament in a general election a year ago.
He apologised in 2012 for breaking his promise on student charges, saying "I will never again make a pledge unless as a party we are absolutely clear about how we can keep it".
"I hope to use some of those skills in my new role".
He will join his Liberal Democrat colleague Richard Allan at the social network. Members of the European Union parliament have called for an audit of Facebook, and careful scrutiny based on competition laws.
"But the key decisions will soon pass to Parliament, of which I am no longer a Member, and once I had chose to take up this unique new challenge at Facebook, I felt it was best to get going sooner rather than later". According to the FT, he will begin work with Facebook over the coming weeks before relocating to Silicon Valley in the new year.
It comes as Mark Zuckerberg seeks to fix the company's reputation amid rows over transparency and the role of "fake news" on the platform following the 2016 Brexit referendum and the election of Donald Trump to US President in 2017.
Mr Schrage will stay as an adviser, Facebook said.
Facebook has faced intense scrutiny and the threat of government regulation following the Cambridge Analytica data scandal and alleged election meddling.