Systems and methods for identifying and transacting with accounts across multiple external systems using inter-system account identifiers, without exposing internal account identifiers of an originating system, are disclosed. An example method, executed by the originating system, includes generating a first and a second inter-system account identifier based on a first and a second request, respectively, received at the originating system from a first and a second external system, respectively, that provide different services to an internal account of the originating system. The first and second inter-system account identifiers are communicated to the first and the second external system, respectively. When a data communication including the first inter-system account identifier and payload data is received from the first external system, the first internal account is retrieved using the first inter-system account identifier, the payload data is associated with the first internal account, and stored in an originating system data store.