The New York defense and spy technology shop had appointed Strianese as its interim CEO when Frank Lanza died in June.
Strianese was also elected to the L-3 board of directors.
"I am honored to receive this appointment from L-3's board. L-3 is a special company and I was privileged to have a key role in its formation and substantial growth over the years and now to carry on the vision that Frank Lanza established and spent the last years of his career realizing, Strianese said in a press release Monday.
L-3 shares closed up 2 cents to $77.68.