The social networking giant's chief operating officer Sheryl Sandberg confirmed the news via a Facebook post describing Clegg, who takes the role of VP for global affairs and communications, as a "thoughtful and gifted leader" and said "his experience and ability to work through complex issues will be invaluable in the years to come.
Clegg served as deputy Prime Minister of the UK when the Liberal Democrats were in coalition with Conservatives between 2010 and 2015, during which time his party pushed forward some policies but was forced to compromise and abandon some earlier pledges, most famously, and perhaps most painfully for the party, scrapping a promise to oppose rises in student tuition fees.
After the 2010 election the Liberal Democrats had 57 MPs; in the 2015 election after being in coalition this dropped to just eight; Clegg lost his seat as an MP in 2017. He will move to California along with his family, Sandberg said.
Hiring Clegg comes at a very difficult time for Facebook, which has been faced with a number of problems.
These ranged from its struggle to deal with fake news, privacy breaches, such as the Cambridge Analytica saga, and its run-ins with regulators, such as being fined €110m by the European Commission last year for providing "misleading information" regarding its takeover of WhatsApp in 2014.
While social media in general and Facebook in particular was once considered mostly harmless or a positive way of making connections, it is now being seen as having significant downsides.
Just this week Facebook was forced into another embarrassing u-turn when i admitted that data from its new Portal home video calling devices may inform ad targeting despite initially saying this was not the case.
While hiring Clegg has surprised many, it does show that Facebook realises it needs to change its approach. Sandberg said that Facebook is on a critical journey. "The challenges we face are serious and clear and now more than ever we need new perspectives to help us through this time of change," she said.
"The opportunities are clear too. Every day people use our apps to connect with family and friends and make a difference in their communities. If we can honour the trust they put in us and live up to our responsibilities, we can help more people use technology to do good."
Clegg said in his own Facebook post that throughout his career he had "relished grappling with difficult and controversial issues and seeking to communicate them to others" and said he hoped to use some of those skills in his new role. He said that while Facebook, WhatsApp, Messenger, Oculus and Instagram are at the heart of so many people's everyday lives they are also at the heart of some of the most complex and difficult questions we face as a society, such as "the privacy of the individual; the integrity of our democratic process; the tensions between local cultures and the global internet; the balance between free speech and prohibited content; the power and concerns around artificial intelligence; and the wellbeing of our children."
Perhaps in a hint at some of what is role will involve he added: "I believe that Facebook must continue to play a role in finding answers to those questions - not by acting alone in Silicon Valley, but by working with people, organizations, governments and regulators around the world to ensure that technology is a force for good."