Google and Facebook team up to offer free, unlimited WhatsApp backups on Google Drive
Also, all WhatsApp backups that haven't been updated in more than one year will be automatically removed from Google Drive storage, so make sure you manually back up your WhatsApp data by November 12 if you don't want to lose it.
Obviously, you'll need a Google account activated on your smartphone with Google Play services installed. Of course, you'll also need enough free space on the smartphone to create the backup. Speaking of creating a backup, here is how it's done: WhatsApp / Menu / Settings / Chats / Chat backup / Back up to Google Drive.
It's important to note that media and messages that you back up aren't protected by WhatsApp end-to-end encryption while stored in Google Drive, so there's that.