Yves Metayer, commander of troop posting at the French Chiefs of Staff, said the scenario called for a major conflict with an unspecified foreign state to be played out.
"The geopolitical context justifies this exercise," Mr Metayer said.
But the said that the war games plan had been in the works since 2020 and followed on from a French strategic review published in 2017.
The review pointed to "a need to prepare for a major conflict", after two decades of mostly asymmetrical warfare with non-state actors, such as militias, he said.
"After the fall of the Berlin Wall, we allowed the mobilisation mechanisms we had during the Cold War to decline," Mr Metayer said.
Between late February and early May, 7,000 troops will play out a sequence involving naval operations in the Mediterranean, and an amphibian and airlift operation in southern France.
This phase will simulate an intervention in a country undermined by militia activity, and neighbour to a powerful nuclear state stirring up the unrest.
From mid-April to early May, the soldiers will simulate an air and land conflict with that powerful state, involving up to 12,000 troops in northern France.
Orion will involve land, sea, air and space parts, including cyber warfare, as well as civilian operations in wartime, such as health services and transport, Mr Metayer said.