Before joining WhatsApp, Arora worked with Google.
"It is hard to believe that it has been seven years since Jan (Koum) and Brian (Acton) got me onboard at WhatsApp, and it has been one hell of a ride," Arora said in a post on Tuesday.
"I am deeply indebted to Jan and Brian, who entrusted me to be their business companion for so many years," he added.
In a jolt to Facebook in May, WhatsApp co-founder and CEO Koum decided to move on amid reports that he had a difference of opinion with parent company Facebook over data privacy, encryption and other issues.
Arora was rumoured to be the frontrunner to replace Koum as CEO.
Another WhatsAppAco-founder Acton made his highly-publicised exit from Facebook in 2017.
"It's time to move on, but I cannot be more proud of how WhatsApp continues to touch people in so many different ways every day," Arora said.
"I am confident that WhatsApp will continue to be the simple, secure and trusted communication product for years to come," he added.
In a statement to IANS, a spokesperson for the popular messaging service said, WhatsApp would remain "committed to providing a way for people to communicate privately now and in the future".
"WhatsApp is grateful for the dedication, focus, and outstanding work of our early leaders and team."
WhatsApp last week named Ezetap Co-founder Abhijit Bose as its India head.
He will build WhatsApp's first full country team outside of California and will be based in Gurugram, the Facebook-owned platform said.
The appointment of Bose as India head came at a time when the popular messaging service, which has over 200 million users in the country, is planning to launch a payment service.