Trinity will use Pluck's SiteLife platform to offer social media tools to strengthen user experience on its websites.
Pluck will be launched on Trinity Mirror's key newspaper sites later this year.
David Black, Trinity Mirror's group director of digital publishing, said: "At the heart of our strategy is providing our users with a really engaging experience online.
"Pluck's leading technology will play an instrumental role in helping us connect with our users.
"By giving social media tools such as user comments, ratings and user profiles a key role on our websites, we will be creating an enhanced experience for our audience, who know they can rely on us to offer the best ways to discuss the most pertinent issues of the day."
Dave Panos, executive vice president of Pluck at parent company Demand Media, said: "Research is showing that those who are embracing social media tools are finding themselves ahead of the competition.
"Pluck's award-winning products will help Trinity Mirror empower its readers with an interactive experience that will keep them engaged, extending loyalty over the long term."