Mailchimp users can directly import their email subscribers from any mailing list in Mailchimp to Google Sheets.
Go to the mail merge menu in Google Sheets and choose Import Contacts > From Mailchimp Lists.
You'll have to authorize the connection so that Google Sheets can read and download your list of email subscribers.
Once the connection is authorized, select your Mailchimp list from the dropdown and choose
Import Contacts to bring all the subscribers into Google Sheets.
If you are using Constant Contact, Active Campaign, Convertkit or another email marketing tool, you can also import email subscribers from those services into the Mail Merge sheet using the CSV import option.