Communicator Corp, based in Sunderland, operates in nearly 180 countries and its client base includes Adidas, Mitchells & Butler and Scottish & Southern Energy.
This latest acquisition follows Trinity Mirror's purchase of digital marketing services specialist Rippleffect in 2008.
Communicator Corp reported revenues of £3.5m and operating profit of £1m in the year ending 31 March 2011.
Trinity Mirror paid for the company in cash.
The publishing group is looking to become less reliant on its core print assets of national and local newspapers.
Sly Bailey, chief executive of Trinity Mirror, said: "Increasingly, we're seeing that, in addition to print and website advertising, clients want help in areas such as website design, search engine optimisation, e-mail marketing, social media and web analytics.
"The addition of Communicator Corp to our stable of digital assets will enhance our offering and complement the digital marketing services currently offered by Rippleffect."
Follow John Reynolds on Twitter @johnreynolds10
This article was first published on mediaweek.co.uk