Shares of LinkedIn surged 47 percent after the announcement to near $193, while Microsoft's stock was down 3.2 percent. Trading in Microsoft had been halted briefly for news pending before the announcement of the all-cash deal.
Moody's Investors Service placed Microsoft's "AAA" rating under review for downgrade following the deal announcement. Standard & Poor's though, reaffirmed its "AAA" rating, and said it maintains all other ratings and a "stable outlook" on the company.
Jeff Weiner will stay on as CEO of LinkedIn and will report to Microsoft CEO Satya Nadella. The deal was unanimously approved by both companies' boards, and is expected to close by the end of the year. The acquisition is still subject to approval by LinkedIn shareholders and regulators.
"The LinkedIn team has grown a fantastic business centered on connecting the world's professionals," Nadella said in a statement. "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."
In a statement to LinkedIn employees, Weiner said "little is expected to change" and employees will have the same titles and managers.
"The one exception: For those members of the team whose jobs are entirely focused on maintaining LinkedIn's status as a publicly traded company, we'll be helping you find your next play," Weiner said. "In terms of everything else, it should be business as usual. We have the same mission and vision; we have the same culture and values; and I'm still the CEO of LinkedIn."
"This is a great deal," said Ivan Feinseth, CIO at investment firm Tigress Financial Partners, told CNBC's "Squawk Box." He said his company publishes research on Microsoft.
"LinkedIn is the ultimate business social platform. You have everybody on this, from interns and college students on up to the biggest CEOs," Feinseth said. "This is a good way for Microsoft to expand in social platforms."
Some analysts had speculated that Microsoft might buy Salesforce.com as a cloud play. Feinseth said an eventual Salesforce.com deal could still happen." Microsoft has the resources ... the cash ... the balance sheet ... and the borrowing ability to acquire a lot more."
Mark Hawtin, investment director at GAM, told CNBC's "Closing Bell" that he thought both companies benefited in the deal.
"[Microsoft] can now provide this social fabric which I think is going to be so important in this network economy," said Hawtin, who owns shares in both companies through his firm's funds. "For LinkedIn, I think it also gives them a chance to have a jump start to move the business more rapidly."
Shares of LinkedIn had peaked in the past year at $258.39. The stock is down more than 14 percent year to date, and 10 percent in the past year. LinkedIn, which has more than 400 million members, acquired online education company Lynda.com last April. It rolled out a new version of its Recruiter product this year, which the company said increased membership, engagement and financial results.
Shares of Microsoft traded near $50 on Monday, down from their 52-week high of $56.85. The company's stock has gained more than 8 percent year over year.
Correction: Microsoft is buying LinkedIn for $26.2 billion. That figure was briefly misstated in one headline reference on an earlier version of this article.