"He's left Microsoft to pursue other opportunities, and we wish him the best in the future," said Microsoft Xbox spokesman James Bernard.
Bernard said the resignation would have no effect on Microsoft's plans for the console. "We're really confident moving forward," he said.
, whose title was chief Xbox technical officer, did not have a high-level position in Microsoft's organizational structure. But he was considered a key element in giving the company credibility with gamers.
The skateboarding, creatively attired Blackley was called on to represent Microsoft at numerous key Xbox events, including the console's public, where Blackley demonstrated games for Chairman Bill Gates.
A veteran of the game development arm of the SKG DreamWorks entertainment studio, Blackley joined Microsoft three years ago, originally to work on DirectX, the library of graphics programming instruction used by most PC games. He was with the company a few months when he proposed the idea of Microsoft making its own game console.
Blackley's spokeswoman told Reuters that Blackley would not be ready to discuss for another two weeks at least the details of the new business venture he is pursuing. She gave no indication as to what type of business the new company would be.
The news of Blackley's resignation comes just a few days after Microsoftit would miss current sales target for the Xbox by 500,000 units or more, a shortfall it blamed on weak sales in Japan and Europe. Microsoft responded by cutting the European price of the Xbox by almost 40 percent.
Microsoft has seen several high-profile personnel changes in recent months, including theearly this month of President and Chief Operating Officer Rick Belluzzo.
Reuters contributed to this report.