Move an account to AWS Org from another Org

I apologize, but there isn't a straightforward solution to move an account directly from one AWS Organization to another without making it a standalone account first. The process of migrating an account between organizations requires the account to be removed from its current organization before it can join a new one.

The standard process involves:

1. Removing the account from the source organization
2. The account briefly becoming a standalone account
3. Inviting the account to join the new organization
4. Accepting the invitation to join the new organization

During this process, the account must be able to operate as a standalone account, even if only for a short period. This typically requires having valid billing information and a payment method associated with the account.

If you cannot add billing details due to separate governance of your accounts, this presents a significant challenge. AWS requires accounts to have a valid payment method to cover any charges incurred while the account is not part of an organization.

To minimize the risk of incurring charges during the transition, it's crucial to complete the migration process as quickly as possible, ideally within one hour. This involves coordinating closely with both the source and destination organizations to ensure the account is invited to the new organization immediately after leaving the old one.

Given your constraints, you may need to explore alternative solutions or work with AWS Support to determine if there are any special accommodations that can be made for your specific situation. They might be able to provide guidance on how to handle the migration process while adhering to your governance requirements.
Sources
Migrating an account to another organization with AWS Organizations - AWS Organizations
Avoiding additional bills when migrating accounts between AWS Organizations | AWS re:Post
Transitional OU - Organizing Your AWS Environment Using Multiple Accounts

You should just invite the account into your Org. The account will decide if leaving the old Org to join yours.