A system and related method for completing online transactions via mobile device includes a client-side e-commerce platform executing on the mobile device that identifies candidate items for purchase based on images related to an item desired by the user. The client-side platform determines attributes of the item based on an image captured by an onboard camera or otherwise stored on, or downloaded to, the mobile device. Purchase information for items offered by participating vendors, or third-party vendors, is retrieved by the platform via APIs of the vendor network or automated middleware respectively. The user may select items for purchase and complete the transaction via single click, and the middleware forwards payment details to the third-party vendors and retrieves purchase information and transaction records from the third-party vendors. The client-side platform generates a single transaction and invoice whether the selected items are purchased from in-network or third-party vendors.