A system and method for authorizing transactions via mobile devices is provided. The system includes a mobile device executing a transaction authorization application. The transaction authorization application generates a transaction code for a transaction upon request by a user. The transaction authorization application includes a presentation module for presentation of the transaction code on the mobile device, and a communication module for communicating at least a part of the transaction code over a first channel. A server is in communication with the mobile device over the first channel for receiving the at least partial transaction code. The server is also in communication with a merchant system over a second channel for receiving a transaction request for the transaction. The transaction request includes the transaction code. The server executes transaction processing software for validating the transaction code received via the second channel by determining if the transaction code received via the second channel matches the at least partial transaction code received via the first channel. The server then communicates a transaction response to the merchant system.