The service currently only offers Sky Movies, but is scheduled to expand next year and include content - live and on demand - from channels such as Sky 1, Sky Arts, Sky Sports and Sky Living.
The launch of the Roku service comes several months after Sky invested $10 million in Roku, as reported here in July.
Viewers will be able to access the service with a Roku box, with the basic 720p model costing from around £49 and via a broadband connection of at least 2Mbps. The service offers a flexible subscription model; however full details of how the service will be priced once additional content goes live is still unknown.
Roku also hosts the Vision TV Network of international TV channels as an alternative route to the service provided on Freeview via a "streaming channel".
- You can read more about Now TV on Roku at http://www.trustedreviews.com/news/sky-s-now-tv-arrives-on-roku-set-top-boxes