Andy Miller, vice president of mobile marketing for Apple Inc., announced Wednesday that he is leaving Apple to join venture capital firm Highland Capital Partners as a general partner. Mr. Miller had been in charge of Apple’s iAd mobile advertising network, reporting directly to CEO Steve Jobs.

Former Apple Vice President Andy Miller

Mr. Miller joined Apple when the Mac and iPhone maker bought Quattro Wireless, which he founded. Apple then used the intellectual property and personnel acquired from Quattro to build and launch iAd, Apple’s first foray into the world of advertising.

iAd delivers ads exclusively to Apple’s iOS devices, including iPhones, iPads, and iPod touches, and Apple has billed its network as offering an enhanced advertising experience for consumers.

Highland Capital Partners is a successful Silicon Valley venture capital firm, and it claims Quattro Wireless—the same Quattro Wireless—among the successful startups it has funded.

“We’ve had the opportunity to work very closely with Andy for years, since the early days of Quattro Wireless and then beyond,” Bob Davis, General Partner with Highland Capital Partners, said in a statement. “Andy understands the entrepreneurial journey and has an incredible network of entrepreneurs and CEO’s in the digital media and mobile sectors. He will be an exceptional addition to Highland.”

Mr. Miller added, “I am excited to join the team and for the opportunity to work with exceptional entrepreneurs building the next generation of innovative, market leading companies.”

This is the third high-ranking executive to leave Apple in the last year. In August of 2010, Mark Papermaster left after just 18 months on the job, while Ron Johnson, the man credited with building Apple’s remarkably successful fleet of retail stores, announced in June of this year that he would be leaving Apple to take over as CEO of J.C. Penney later this fall.