So much for all the talk last week about interim CEO Ross Levinsohn landing the top job on a more secure basis. Mayer, 37, was the 20th employee at Google — and emerged as one of the company’s most prominent representatives. An engineer, she was credited with developing the look and feel of its most popular products including Google Maps. But her path to the top seemed blocked by the presence of Google’s co-founders Sergey Brin and Larry Page. The news of her appointment sent Yahoo shares up about 2% in after-market trading. Investors shouldn’t expect miracles: Yahoo has been struggling to find its place in the Internet advertising universe against Google and Facebook and other content providers. The company has been seen as a jack of all trades, with several compelling services — but no clear mission. The company’s stock has lost about 41% of its value over the last five years and has been stagnant lately. Last year the company ousted Carol Bartz from the top job. Her successor, Scott Thompson, was forced out in May after a dissident shareholder disclosed that he had exaggerated his college credentials. Third Point CEO Daniel Loeb, who led the attacks on Yahoo’s management, was added to the board along with two colleagues after he threatened to wage a proxy fight. Here’s today’s release:

SUNNYVALE, Calif., Jul 16, 2012 — Yahoo! today announced that it has appointed Marissa Mayer as President and Chief Executive Officer and Member of the Board of Directors effective July 17, 2012. The appointment of Ms. Mayer, a leading consumer internet executive, signals a renewed focus on product innovation to drive user experience and advertising revenue for one of the world’s largest consumer internet brands, whose leading properties include Yahoo! Finance, Yahoo! Sports, Yahoo! Mobile, Yahoo! Mail, and Yahoo! Search.

Mayer said, “I am honored and delighted to lead Yahoo!, one of the internet’s premier destinations for more than 700 million users. I look forward to working with the Company’s dedicated employees to bring innovative products, content, and personalized experiences to users and advertisers all around the world.”

Most recently, Mayer was responsible for Local, Maps, and Location Services for Google, the company’s suite of local and geographical products including Google Maps, Google Earth, Zagat, Street View, and local search, for desktop and mobile. Mayer joined Google in 1999 as its 20th employee and led efforts for many of Google’s most recognizable products, including the development of its flagship search product and iconic homepage for over 10 years. Mayer managed some of Google’s most successful innovations, launching more than 100 features and products including image, book and product search, toolbar, iGoogle, Google News, and Gmail – creating much of the “look and feel” of the Google user experience.

Yahoo! Co-Founder David Filo said, “Marissa is a well-known, visionary leader in user experience and product design and one of Silicon Valley’s most exciting strategists in technology development. I look forward to working with her to enhance Yahoo’s product offerings for our over 700 million unique monthly visitors.”

“The Board of Directors unanimously agreed that Marissa’s unparalleled track record in technology, design, and product execution makes her the right leader for Yahoo! at this time of enormous opportunity,” said Fred Amoroso, Chairman of the Board of Directors.

Mayer received her B.S. in Symbolic Systems and her M.S. in Computer Science from Stanford University, specializing in artificial intelligence for both degrees. She is credited as an inventor on several patents in artificial intelligence and interface design.

“Yahoo!’s products will continue to enhance our partnerships with advertisers, technology and media companies, while inspiring and delighting our users. There is a lot to do and I can’t wait to get started,” Mayer said.

Related: Yahoo Board Likely To OK Ross Levinsohn As CEO: Reports