A method for atomic exchange of assets on multiple blockchains using transient key pairs includes: generating, by a first computing device, a proposal message, the proposal message including at least a first transaction value, a first network identifier corresponding to a first blockchain, a second transaction value, a second network identifier corresponding to a second blockchain, and a swap public key of a swap cryptographic key pair; generating, by the first computing device, a first digital signature for the proposal message; encrypting, by the first computing device, the first digital signature using the swap public key and a first private key of a first cryptographic key pair; appending, by the first computing device, the encrypted first digital signature to the generated proposal message; and transmitting, by the first computing device, the generated proposal message with appended encrypted first digital signature to a second computing device.