Please follow these steps to link your Runic and Steam accounts:
- Launch Torchlight II
- Click the 'Log In' button located in the lower right corner of the title screen
- Click the 'Manage Account' button which should open the Runic account manager website in your default browser
- Either register a new Runic account or log in with an existing one
- Click 'Register Torchlight II for Internet Play' or 'View My Product Keys'
- Click 'Link My Steam Account' or 'Check My Steam Account For Games'
- Follow the remaining on-screen instructions to complete the process