It's not the first time a major corporation or non-profit has poached a former political leader to offer clarity on the inner workings of government. After wrapping up his work as president of the European Commission, Jose Manuel Barroso joined Goldman Sachs as non-executive chairman in 2016.
Former German chancellor Gerhard Schroeder went on to chair oil company Rosneft; former UK Foreign Secretary David Miliband moved to New York to become CEO of the International Rescue Committee.
Tech companies have been poaching British talent for years as well, though Clegg appears to be the highest-ranking departure to date. Steve Hilton, a former director of strategy to ex-Prime Minister David Cameron, decamped to California and now hosts a Fox news show.
Tim Chatwin, another Cameron aide, now works for Google, as does Theo Bertram, who worked in Downing Street for Labour Party Prime Ministers Tony Blair and Gordon Brown.
Clegg led the Liberal Democrats from 2007 to 2015, including five years in the coalition government with the Conservatives.
He lost his seat at last year's general election. Before that, he was a member of the European Parliament from 1999 to 2004.
In recent months, he has been an active campaigner for a second referendum on Brexit, in hopes of preventing Britain's departure from the EU.
Clegg argued that supporters of Brexit failed to explain the sacrifices that will follow an exit, but he said it was nonetheless time for him to go.
Clegg, who starts Monday, said that he and his family will be moving to California to take on the new job in the coming year. He had been discussing a new role with Sandberg and CEO Mark Zuckerberg over the summer.
Sandberg also posted a welcome to Clegg on Facebook which also echoed his comments that technology can be used "to do good."
"Our company is on a critical journey," she wrote. "The challenges we face are serious and clear and now more than ever we need new perspectives to help us though this time of change."
- AP