Facebook Messenger has supported video calling since April, but now the app lets one person stream live video in a conversation while the other watches.
The new feature, which Facebook is calling Instant Video, will be available through an update to the Messenger app on Thursday.
"It's perfect for sharing quick moments with friends who aren't right by your side or making your conversations richer by seeing each other face-to-face when you are messaging," Facebook said on its company blog.
Once you're using the new version of Messenger, you'll be able to start a one-way video stream with someone by tapping on the video icon at the top right of a conversation thread. Streams will start with sound off by default, and the video feed will be shown in a small thumbnail so you can still see what your friend is typing.
Instant Video in Messenger is the latest example of how Facebook can't seem to stop borrowing from Snapchat. The Snapchat app has offered one-way video streaming in its chat interface for a long time and more prominently positioned the feature in March.