After previously only existing as an "Easter Egg" setting, Facebook in April 2019 added a Dark Mode theme as an official display feature of its standalone Messenger app.
Facebook says that Dark Mode is designed to provide less harsh brightness in situations where ambient lighting is lower while maintaining contrast and vibrancy.
If you have an OLED iPhone, such as an iPhone X, iPhone XS, or iPhone XS Max, enabling Dark Mode can also conserve battery life, since black pixels in an OLED panel basically switch off and consume far less power.
Enabling Dark Mode in Facebook Messenger is easy – simply follow the steps below.
- Launch the standalone Messenger app on your iPhone.
- Tap your profile picture in the top-left corner of the screen.
- Toggle the Dark mode switch to the green ON position.
And that's all there is to it. If you don't see the Dark Mode switch in the settings menu, try force-quitting the iPhone app and launch it again, then follow the steps above.