An affiliate of Platinum Equity agreed to buy Wesco Aircraft Holdings Inc., a distributor of aviation and defense parts, for $1.1 billion.

Wesco shareholders will get $11.05 a share in cash, a 14% premium over the closing price May 24, the last trading day before media speculation about a potential transaction. When the deal closes, the Valencia, Calif.-based company will be combined with Pattonair, a Platinum Equity business, Wesco said in a statement Aug. 9.

The deal boosts Platinum’s exposure to the burgeoning aerospace industry, which is benefiting from rising air travel worldwide. Wesco, which counts Carlyle Group LP and...