The former Prime Minister is currently working on his memoirs after quitting No 10 and his role as an MP last year.
He has also taken on a number of lucrative speaking roles, with one report suggesting he is charging over £100,000 an hour.
Mr Schwarzenegger was in the audience in California after the former PM gave a talk on globalisation at the University of Southern California on Thursday.
Appearing in a Snapchat video with Mr Schwarzenegger, Mr Cameron described his A-list companion as “the governor”.
He added: “He did a great job, and I’ll be back.”
David Cameron and Arnold Schwarzenegger pose for a Snapchat video
During his talk Mr Cameron, whose relentless fear-mongering and negative campaigning during the referendum contributed to him quitting No 10, called for optimism.
According to the Daily Trojan, Mr Cameron told the assemble audience: “Sometimes it’s good to stand back and take a look across the decades and see what has been achieved.
“Almost a billion people in the world have been taken out of poverty, diseases like polio almost eradicated from the face of the earth. And democracy is still on the march.”
On the subject of Brexit and the campaign, Mr Cameron added: “The argument for staying in [the European Union] was not one of emotion, but of utility, for the influence we gain and the economic benefits of trade and cooperation.
“In the future we will be out of the European Union, but hopefully taking part in the things we need, such as a strong trade relationship and security.
David Cameron and George Osborne on the 2015 campaign trail
He did a great job, and I’ll be back
Get Quotes on Home Insurance
“If those pursuing Brexit are for cutting Britain off from the world, I wouldn’t worry, for that is not the role of Prime Minister May’s government.”
Mr Cameron’s vow to “be back” could mean there is truth to the speculation of him landing a plum role with Nato as Secretary General.
A source recently told the Daily Mail that Mr Cameron, 50, was under consideration for Europe’s top defence posting.
David Cameron stands down as MP Mon, September 12, 2016
David Cameron has served as Prime Minister since 2010 and leader of the Conservative Party since 2005. We take a look at his political career in pictures.
Getty Images 1 of 103
Prime Minister David Cameron with his wife Samantha leave 10 Downing Street for the last time after speaking to the press to visit Buckingham Palace to formally tender his resignation to the Queen on July 13, 2016
The role offers a tax-free salary of £220,000 with the incumbent Jens Stoltenberg, expected to finish his term in either 2018 or 2019.
While still an MP, Mr Osborne has had no qualms with taking a lucrative job with US financial giant BlackRock.
The former Chancellor is expected to earn large six-figure sum from his work with the world’s largest asset manager.
- What is Brexit? What happens now Britain has voted to leave the EU?
- Teenager thanks drug addict mum and dad in amazing open letter
- GET OVER IT: Remoaners told to ACCEPT Brexit as 'it's not a disaster'