The partnership forms part of MGN Digital's strategy, which aims to place video at the heart of its websites.
From February, the homepage will host three embedded video players featuring its core content categories of news, sport and showbiz. As visitors move through the site they will be able to select video items from an integrated menu, and the page will be transformed by a unique slide-down screen to reveal Mirror Player.
Advertisers will also be able to purchase pre-roll video and banner ad formats that can be synchronised by campaign, and will eventually be available across all of MGN Digital's video channels.
The partnership will include deliver up-to-the-minute video content delivered through Roo's unique Video Exchange and individual sites will also produce their own video content.
Julia Smith, head of digital at MGN, said: "Through our partnership with Roo we have received access to the most sophisticated video streaming technology on the market. Roo is the perfect choice for online publishing, as its depth of content reflects exactly what our readership desires."
Robert Petty, CEO of Roo, said: "The British public has a tremendous appetite for online video, and traditional news organisations are realising the importance of providing a greater interactive experience to their online audiences."
Earlier this week, News Corp announced it was to become a strategic investor in Roo Group, which already handles video distribution for the publisher's The Times and The Australian online versions.
News Corp has taken up to 5% stake in Roo and up to an additional 5% interest if the publisher meets specific revenue targets by using Roo Group's products and services.
Roo also works with sites such as portal lycos.co.uk, The Financial Times and Sky News.