Mayer joined Google in 1999 as its 20th employee and went on to play an integral role in helping Page and Brin exploit their online search technology to outmaneuver Yahoo at a time when it was still the larger of the two companies. Now, it takes Google a little more than a month to generate as much revenue as Yahoo does in an entire year.
During Google's rise, Mayer helped oversee the development and design of the company's popular email, online mapping and news services. She also became a topic of Silicon Valley gossip during Google's early years while she dated Page for three years. They have since gotten married to other people.
"We will miss her talents," Page, now Google's CEO, said in a statement.
In another statement, Schmidt hailed Mayer as "a great product person, very innovative and a real perfectionist who always wants the best for users. Yahoo has made a great choice."
Mayer becomes one of the most prominent women executives in Silicon Valley, a place whose geeky culture has been dominated by men for decades. This is Yahoo's second female CEO, though. Silicon Valley veteran Carol Bartz, 63, spent more than two-and-half years as Yahoo's CEO before she was fired last September.
Within a few months, Mayer expects to be on a maternity leave. In another interview late Monday, Mayer revealed to Fortune magazine that she is pregnant with a boy. Her due date is Oct. 7. She said she had informed Yahoo's board about her pregnancy before the 11 directors unanimously voted to hire her.