Under the deal, Rockwell shareholders will receive $140 per share in stock and cash, split between $93.33 in cash and $46.67 in United Tech stock, the companies said in a statement.
The offer represents an 18 premium to Rockwell's closing share price on Aug. 3, the day before media reported that UTC was weighing a bid for Rockwell.
Under the deal, the companies said that Rockwell Collins and UTC's aerospace systems segment will be combined to create a new business unit named Collins Aerospace Systems.
"This acquisition adds tremendous capabilities to our aerospace businesses and strengthens our complementary offerings of technologically advanced aerospace systems," UTC's chairman and chief executive officer, Greg Hayes, said in the statement.
"Together, Rockwell Collins and UTC Aerospace Systems will enhance customer value in a rapidly evolving aerospace industry by making aircraft more intelligent and more connected," he said.
The deal, which includes $7 billion in Rockwell's debt, is expected to save more than $500 million by the fourth year after its completion, the companies said.
Morgan Stanley & Co was the financial adviser to United Tech and Wachtell, Lipton, Rosen & Katz was its legal adviser.
J.P. Morgan Securities LLC and Citigroup Global Markets Inc were Rockwell's financial advisers, while Skadden, Arps, Slate, Meagher & Flom was its legal advisor.