Microsoft Corp agreed to buy LinkedIn Corp for $26.2 billion in cash, the companies said in a statement on Monday.
The offer of $196 per share represents a premium of 49.5 percent to LinkedIn's Friday closing price.
"Today is a re-founding moment for LinkedIn," Reid Hoffman, chairman of LinkedIn's board, said in a statement.
Jeff Weiner will remain chief executive of LinkedIn, reporting to Microsoft CEO Satya Nadella.
The deal is expected to close in 2016.
"The LinkedIn team has grown a fantastic business centred on connecting the world's professionals," said Satya Nadella, Microsoft's chief executive.
"Together we can accelerate the growth of LinkedIn, as well as Microsoft Office 365 and Dynamics as we seek to empower every person and organization on the planet."