Game of Thrones Ascent, the online videogame created by Boston developer Disruptor Beam, could soon attract a much larger audience thanks to a deal with casual gaming giant Zynga Inc. of San Francisco. The game, based on the popular HBO television series, is currently available on Facebook and gaming site Kongregate.com. Now Zynga has agreed to offer Game of Thrones Ascent on its own Zynga.com website, and to promote the game to millions of people who play Zynga’s games on Facebook.

The deal reflects a strategy shift at Zynga. While the company claims to attract 250 million gamers every month, the popularity of its games has recently waned, and first-quarter revenues were down 18 percent from the same period in 2012.

Last October, Zynga shut down its offices in Cambridge, laying off about 45 workers. The company hopes to rebound by doing more deals with outside game developers like Disruptor Beam, who can help Zynga quickly upgrade its roster of games.

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Nearly one million people have signed up to play Game of Thrones Ascent since its debut in February.