The acquisition was originally announced in February.
Based in the US, Gibbs & Cox is an independent ship design firm engaged in naval architecture and marine engineering.
Gibbs & Cox will be merged with Leidos’ maritime systems division and function as its fully owned subsidiary.
The acquisition enables Leidos to provide a wide range of engineering solutions to the US Navy and to an expanding number of foreign navies.
Leidos chairman and CEO Roger Krone said: “We are delighted to welcome the Gibbs & Cox team to the Leidos family.
“Gibbs & Cox is widely regarded for developing the most talented and experienced naval designers in the world.”
Leidos appointed Citigroup Global Markets as exclusive financial advisor and Holland & Knight as legal advisor for the transaction.
Meanwhile, Houlihan Lokey acted as exclusive financial advisor and Greenburg Traurig as legal advisor to Gibbs & Cox for the deal.
Gibbs & Cox president and chief executive Chris Deegan said: “We are excited to join Leidos, whose employee culture and history of innovation strongly mirror our own legendary 91-year history.
“Gibbs & Cox will remain the nation’s largest independent provider of maritime services. The combination of our world-class naval architecture, design and engineering services with Leidos’ speed, security and scale will significantly enhance our combined offerings in the fast growing maritime undersea, autonomous and cyber security segments.”