Larry Page to become Google chief executive
He will take over from Eric Schmidt, who has been in the job for a decade and will become executive chairman.
Google said Mr Schmidt would focus on "deals, partnerships, customers and broader business relationships".
The surprise news came as Google unveiled a strong rise in net profits in the last three months of $2.54bn (£1.6bn) on revenues of $8.44bn.
Mr Page, 37, is reclaiming the job he relinquished to Mr Schmidt, 55, when investors called for a more experienced business leader.
"In my clear opinion, Larry is ready to lead and I'm excited about working with both him and Sergey [Brin] for a long time to come," Mr Schmidt said in a blog posting. Mr Brin, also 37, is Google's other founder.
Mr Schmidt said the management changes, which take effect on April 4, were part of a plan to "streamline" decision making and create clearer lines of responsibility and accountability.
"We've been talking about how best to simplify our management structure and speed up decision making for a long time," Mr Schmidt said.
He added: "Larry will now lead product development and technology strategy, his greatest strengths... Sergey has decided to devote his time and energy to strategic projects, in particular working on new products. His title will be co-founder"; Kazinform cites BBC News.
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