It isn't clear what future plans the executives have.
In his blog post, Zuckerberg said that Cox had told him that he planned to move on several years ago, but that Cox chose to hold off on leaving until the company made more progress combating misinformation and Russian meddling - controversies that erupted in the wake of the 2016 election.
Zuckerberg phrased that more delicately, noting that "We both realized we had too much important work to do to improve our products for society".
Zuckerberg said on Thursday that Olivan will now lead the effort to integrate Facebook apps, a key move as the company encrypts conversations on more of its messaging services and makes them compatible.
Cox, who grew up in Winnetka and graduated from New Trier in 2000, has been with Facebook since the company's early days.
Facebook Chief Product Officer Chris Cox (left) is leaving the social media company.
Reversing course, Facebook will not appoint a direct replacement for Cox. It's a huge job for Zuckerberg and all the leaders of Facebook's apps, so it's not going to be an easy job for anyone involved.
Their departures come barely a week after Zuckerberg announced sweeping changes to Facebook, in order re-orient the social network around encryption and privacy.
Numerous changes Zuckerberg outlined involve duplicating some of WhatsApp's features in Facebook's other messaging apps.
Daniels has been at Facebook almost nine years, and previously led the company's Internet.org effort, a project aimed at bringing internet access to developing countries.
It is also interesting to see the head of WhatsApp Chris Daniels leaving Facebook right now.
Daniels took over the leadership of WhatsApp a year ago after the founders of the service, Jan Koum and Brian Acton, left Facebook, citing directional disagreements with Zuckerberg.
While Zuckerberg also said that Cox had spoken before about his desire to leave the company, that his departure is tied directly to Facebook's so-called privacy pivot, is significant.