The deal "creates the leading global research and advisory company for all major functions in the enterprise," the companies said in their joint statement.
Gartner anticipated the deal would be immediately accretive to its adjusted earnings per share and projected a double-digit percentage accretion in 2018.
Shares of Gartner, a Stamford, Conn., information technology research firm, tumbled about 8.8% to $92.83 in afternoon trading Thursday following the announcement, with more than 2.9 million shares trading hands. The stock is up roughly 2.4% since last January.
Meanwhile, shares of Arlington, Va.-based CEB had soared about 21.2% to $75.05 on Thursday, with roughly 3.1 million shares trading. The shares have gained 26.9% since the start of 2016.