Corps Security has won a five-year contract worth £3.6 million annually to provide security services to Tata Steel Europe across the UK.
Tata is Europe's second-largest steel producer with operations in 26 countries and a commercial presence in more than 50 countries.
Corps will provide more than 100 security officers to secure all 14 of Tata's UK sites, including the flagship steelmaking plant in Port Talbot, Wales.
Mike Bullock, CEO of Corps Security, said: "The Tata Group was founded on the principle that its activities should always benefit society and is majority owned by philanthropic trusts. As a trust that was set up in 1859 to provide employment for ex-servicemen returning from the Crimea, we share their values and look forward to working closely together."