Ranger Mathieu Shamavu says the picture was taken at Virunga National Park, a UNESCO World Heritage Site in the Democratic Republic of Congo.
A spokesperson for the park told Sky News the pair both lived in a specially designed unit which cares for gorilla orphans who have been victimised by poachers or animal traffickers.
Mr Shamavu described his captivating composition as just “another day in the office”.
He is part of the park’s Elite Anti-Poaching Units And Combat Trackers group, which is tasked with protecting the animals.
A team of more than 600 rangers undergoes “intensive training, risking their lives on a daily basis to safeguard the park’s exceptional wildlife”, according to the Virunga National Park website.
Around one third of the world’s population of critically endangered mountain gorillas live in the park’s lush volcanic forests.
The rangers have previously posted several photos of them exceptionally close to gorillas.
A Virunga National Park spokesperson said the pair were “friendly” because they were used to human contact in the Senkwekwe Centre for Gorilla Orphans.
Yvonne Ndege, a spokesperson for UNHCR Kenya, re-posted the image on Twitter, writing: “Selfie of the Year no question!”
Thousands of people responded to the image on Facebook, with one user saying: “Wow, that is an awesome office you’ve got there. Stay safe and thank you for the amazing work you do.”
Another user simply said: “Now that’s a selfie!”
With the photograph being shared thousands of times across social media, supporters have urged people to “make a difference” and donate to Virunga’s conservation efforts.