Halo 3 is the final installment of Microsoft's flagship video game franchise in which players assume the role of a futuristic soldier trying to turn the tide in a war against an alien army.
The game is expected to be a potent weapon for Microsoft as it fights Sony and Nintendo for dominance in the $30 billion global video game industry.
The first "Halo" launched alongside the original Xbox in November 2001 and helped the newcomer console gain a foothold in the market.
Halo 2 debuted in November 2004, racking up $125 million in sales in its first day and cementing the popularity of the Xbox Live online service that lets players compete against each other in frenetic "death match" sessions.
By moving up the launch of Halo 3 to the month of September, Microsoft is betting it will spur sales of Xbox 360 consoles, giving it a larger user base in time for the year-end holiday season that is the high tide for video game sales.
"This is going to be a critical holiday for us versus Sony, especially on the console generation side, and they don't really have an answer for Halo 3," Shane Kim, head of Microsoft Game Studios, said in an interview.
"Given that, I suspect Halo 3 to drive a lot of Xbox 360 sales and Xbox Live memberships," Kim said. "I think at those midnight (launch) events, there are going to be a lot of people walking out with an Xbox 360 along with their copies of Halo 3."
The game will go on sale in Europe on September 26, but Kim said Microsoft had not set a date for Japan, where the Xbox 360 has been eclipsed by Nintendo's Wii and Sony's PlayStation 3.
Kim reiterated his view that Halo 3 would enjoy a bigger launch than Halo 2, saying the number of people who had already paid some money to ensure they can get a copy at launch--known as pre-ordering--was "pretty encouraging."
The regular edition of Halo 3 will sell for $60, with two limited editions going for $70 and $130.
Microsoft set the clock ticking toward the Halo 3 launch on the eve of a large public test of the game that starts on Wednesday and is scheduled to run for about three weeks.
Kim said several hundred thousand people had signed up for the test, or beta, which is intended to work out any remaining kinks in the game and make sure the Live network can handle thousands of matches at the same time.