Mosseri replaces Instagram co-founders Kevin Systrom and Mike Krieger who abruptly announced their departure in September.
“We are thrilled to hand over the reins to a product leader with a strong design background and a focus on craft and simplicity, as well as a deep understanding of the importance of community,” Systrom and Krieger wrote in a blog post late on Monday.
Mosseri began his career as a designer, managed his own design consultancy, and then joined the Facebook design team in 2008.
He moved from design into product management, and spent time working on Mobile then News Feed and most recently, to Instagram.
In the new role, he will oversee all functions of the business and will recruit a new executive team, including a head of engineering, head of product and head of operations.
“We remain excited for the future of Instagram in the coming years as we transition from being leaders at Instagram to being just two users in a billion,” the co-founders said.
Instagram co-founders resigned at a time when social media platforms, including Facebook were facing intense scrutiny over the spread of fake news and sinister campaigns.
Founded in 2010, Instagram was bought by Facebook for $1 billion in 2012.
Instagram’s meteoric rise continued after the acquisition, dwarfing the stagnant growth rates of Snapchat and Facebook.
“We’ve grown from 13 people to over a thousand with offices around the world, all while building products used and loved by a community of over one billion. We’re now ready for our next chapter,” the co-founders said.