The direct answer: Microsoft does not offer an account merge feature. You cannot combine two Microsoft accounts into one, transfer purchases between accounts, or consolidate game libraries, subscriptions, or OneDrive storage from multiple accounts.
This is a frequently requested feature that Microsoft has not implemented.
What you can do instead
Transfer content manually: Files stored in OneDrive can be downloaded from one account and uploaded to another. This works for documents, photos, and general files. It doesn’t work for digital purchases (games, apps, Office licenses) which are tied to the purchasing account.
Choose one account as primary: Decide which account to keep active for everything going forward. Sign in to services, devices, and apps with that account consistently.
Add an email alias: If you want to be able to sign in with multiple email addresses, you can add email aliases to one Microsoft account. Go to account.microsoft.com > Your info > Manage how you sign in to Microsoft > Add email. You can sign in with any alias, but it’s still one account.
Migrate Xbox game library: Xbox purchases are non-transferable between accounts. There’s no official path to move game purchases. Microsoft support has occasionally helped in specific circumstances (fraudulent purchases, account recovery situations) but it’s not a standard service.
Microsoft 365 / Office: Office licenses are tied to the purchasing account. You can add additional accounts to Office’s activation, but you can’t transfer the license itself.
The practical path
Pick the account with the most valuable content (purchased games, important OneDrive files, active subscriptions) as your primary. Transfer files from the secondary to the primary via download/upload. Accept that digital purchases on the secondary account stay on that account unless you continue to use it for those specific services.
If both accounts have Xbox Game Pass or similar subscriptions, let the cheaper or less important one lapse when it renews.