Where is this in the home? You have pretty obvious water damage and intrusion. Your "repair" is going to involve some selective demolition further back to fix these issues before attempting any sort of cosmetic fix.

The basement. The water is no longer coming in a previous owner resolved that issue, but as you are saying, I think more needs further ex’s than just that spot. There is cement behind the wall if that helps.

Is there framing behind there or the drywall is nailed to furring strips. Also if that drywall is in direct contact with the concrete floor, you will get this type of moisture issue.

As millworkman suggested open up a little more and see what's behind there.

Drywall Repair Patch

Sold in larger and smaller sizes also.