The agencies will use the Unreal engine - built by Epic Games - to design law enforcement and military training programs.
Epic and partner Virtual Heroes said the deal included a long-term agreement to support the technology across a number of platforms, including web browsers, consoles, and handheld devices.
Although financial details were not disclosed, a previous statement from DARPA implies the lucrative deal may well be worth over $10 million.
According to the BBC, the game engine will be used to code "serious" training scenariois and environments.
For example, the FBI Academy at Quantico plans to develop a multiple player crime scene that will help agents prepare for various operations.
Similarly, the US Army is slated to build a number of simulations that will allow medics to practice treating the wounded in various battle conditions. Meanwhile, weapons researchers plan on using the platform as an advanced visualization and design tool.
It's probably also worth noting that Virtual Heroes used the Unreal engine to power America's Army 3, a fast-paced FPS promoted by the Army as a recruiting tool. In addition, the engine powers Zero Hour, which helps emergency workers train for terror attacks and other incidents with massive numbers of casualties.
Clearly, computer simulations and games have become a very important training tool for military and emergency responders. To be sure, modern video games are often more realistic than dedicated and highly expensive simulators.