Her hiring signaled the Internet company is likely to renew its focus on the Web technology and products rather than beefing up online content.
Mayer, Google's 20th employee and first female engineer, has led a number of its businesses, and was credited for envisioning the clean, simple Google search interface still in use today, a major selling point for Web surfers.
Also known for her love of fashion and a regular on the society pages, she joins the extremely thin ranks of female Silicon Valley CEOs and told Reuters that she was immediately interested when Yahoo's board reached out to her in mid-June.
“This is a very competitive and a tough space. I don’t think that success is by any means guaranteed,” she said. “My focus is always end-users, great technology and terrific talent.”
Shares of Yahoo, worth less than half their value during its dotcom heyday, gained 2% to $15.9 in after-hours trading.
However, Mayer’s ascension comes as her profile at Google appeared to have diminished in recent months. Shortly after Larry Page took over the helm from Eric Schmidt, she was excluded from a group of top executives reporting directly to the CEO and granted oversight over major strategic decisions.
Google's executive chairman Eric Schmidt said Mayer’s hiring was a “real win” for Yahoo.