Gallagher said Sleeping Dogs, developed by United Front Games, continues to see more than 500,000 people playing it every month.
Reaching profitability was a "critical milestone" for the game, Gallagher said. He did not share a sales figure for the game, though Square Enix previously said it had shipped 1.5 million copies.
"It also shows that we are creating content which is keeping millions of people entertained enough to want to spend their time in our world," he said.
Square Enix purchased the rights to Sleeping Dogs, then named True Crime: Hong Kong, from Activision after the Call of Duty and Guitar Hero publisher canceled the game in 2011.
Gallagher also revealed that Just Cause 2, now more than three years old, still has over 500,000 "active and unique" players per month.
The executive admitted that Square Enix "walked away too early" from these games, noting players would have enjoyed new content or deeper experiences in those gameworlds.
To that end, Gallagher said Square Enix will in the future invest in games with more persistent online worlds.
"We see the opportunity for some of our games continuing beyond a traditional beginning, middle, and end," Gallagher said. "We can have them become extendable and more persistent--with an opportunity to build and grow across games. To design in a way to keep our games alive for years instead of weeks."
"I'm not talking about an MMORPG, although the concept is similar. I'm talking about creating persistent online experiences built on the foundations of the games we are well known for," he added.
Gallagher tempered his comments by saying this approach will not apply to every game, though the company hopes to develop more connected and engaging gameworlds overall.