Before proceeding, make sure you have installed WhatsApp version 2.19.221 or above by heading over to the WhatsApp page on Google Play.
1. Open WhatsApp > tap the vertical three dots icon on the top-right and go to Settings.
2. Go to Account > Privacy > Fingerprint Lock.
3. On the next screen, turn on Unlock with Fingerprint.
4. Additionally, you can also set the duration after which you'll have to use your fingerprint to unlock WhatsApp. It can be set to Immediately, After a minute or After 30 minutes.
5. Further, you can also choose if you want to show the message content and sender in the notifications or not.
Now whenever you open WhatsApp, depending on the automatic lock duration you've set, you will need to apply your fingerprint to unlock the app. And that's how you can set WhatsApp fingerprint lock on your Android smartphone.