News Corp, which owned Rotten Tomatoes through a division called IGN Entertainment, will retain a minority stake in the merged company.
Terms of the deal were not disclosed.
The database will have more than 250,000 movies, 2.3 billion user reviews, half a million reviews by critics and more than 20,000 trailers and videos.
An estimated 30 million visitors are expected to access it monthly via the Internet, handheld devices and other platforms.
To use movie terminology, we think this is a blockbuster double-bill, Flixster's Chief Executive Joe Greenstein said in a statement. It's a huge step forward in our goal of connecting users to their own personalized world of movies on any platform they choose.
The deal follows other actions by IGN to focus on expanding its suite of videogames.
Rotten Tomatoes assigns a score to a movie based on the positive and negative reviews it receives. Many moviegoers rely on its Tomatometer rating to decide what they should watch. (Reporting by Jui Chakravorty)