More than 6,000 companies use ExactTarget, which like Salesforce.com uses cloud technology, allowing companies to manage their digital marketing online.
ExactTarget's clients include Coca-Cola Co., Gap Inc. and Nike Inc., and will provide Salesforce.com the opportunity to more closely tie marketing to social media, where people trade ideas or follow trends.
Salesforce.com will pay $33.75 per share. That's a 53 percent premium to ExactTarget's Monday closing price of $22.10. The companies put the deal's value at approximately $2.5 billion.
The company has targeted the cloud marketing space for acquisitions as grows increasingly important to corporations. Salesforce.com bought Buddy media last year.
The buyout announced Tuesday has been approved unanimously by the boards of both companies and is expected to close by July 31.
Industry watchers like Roth Capital Partners said the deal strengthens the cloud marketing ability of salesforce.com, and pushes the company closer to its goal of topping $1 billion in annual revenue from that source.
"The fit is excellent not only because ExactTarget offers complementary products but also in that ExactTarget has a pure cloud solution with leading market share," said Roth analyst Nathan Schneiderman.
Salesforce.com said that the acquisition is expected to lower its fiscal 2014 adjusted earnings by about 16 cents per share and increase its revenue by $120 million to $125 million. Adjusted earnings are now expected in a range of 31 cents to 33 cents per share on revenue between $3.96 billion and $4 billion.
Analysts expect earnings of 48 cents per share on revenue of $3.87 billion.
The transaction is predicted to reduce second-quarter adjusted earnings by approximately 5 cents per share, with results now anticipated between 6 cents to 7 cents per share.
Wall Street expects earnings of 12 cents per share.
ExactTarget Inc. has about 69.3 million outstanding shares, according to FactSet. The Indianapolis company's stock jumped 53.3 percent in Tuesday premarket trading.
Shares of Salesforce.com Inc., based in San Francisco, fell more than 2 percent before the market opened.