If your institution utilizes Microsoft accounts, or you are unable to create a Gmail account, you can use an existing account to create a Google account.
Note: Creating a Google account does not create a Gmail account.
Creating a Google account with existing email
1) Visit: https://accounts.google.com/SignUp
Enter name + basic information
Use existing email address (your professional email address)
Enter your existing (non-Google) email. Check your email and copy the verification code.
2) Verify your email
Check your non-Google email. You should have received an email from Google with a verification code. Copy the verification code and complete your Google Account registration.
3) Finish setting up your Google account
Create a password and follow the steps to finish setting up your Google account.
You can now use your non-Google email to access your Google account.