The same full ecumenical council, I suppose, that ratified the Protestant canon. ;)
We believe the Holy Spirit ratified the protestant canon. But Athanasius gives us the 367 date that confirms when the current canon was almost universally accepted. We believe that the recognition of the established canon was a gradual process as some books of scripture were much more widespread and well known and accepted than others that were just not as well known. About 75% of the current canon was widely accepted by mid 2nd century as established by the Mauritanian canon.