BuddyPress Auto Join Groups

BuddyPress Auto Join Groups helps site admins to automate group joining for members. You can create one or more auto group join lists with conditions, and any user matching those lists will be added to the specified groups.

The plugin can be used to create global lists as well as conditional lists.

A global list is a group list without any conditions. All users are considered a match for this type of list. Any user joining the site will be added to the groups specified in these lists(Yes, you can create multiple global group lists if you need to).