Sir Stuart Peach is expected to be named as the new Chief of the Defence Staff.
He is currently the vice chief, a role which involves deputising for the head of the Armed Forces.
Air Chief Marshal Sir Stuart is reported to have been among three candidates for the top job, being chosen over First Sea Lord Admiral Sir George Zambellas and General Sir Richard Barrons.
Sir Stuart is expected to take over from the current Chief of the Defence Staff General Sir Nicholas Houghton later this year.
The father-of-two from the West Midlands was commissioned into the RAF in 1977, and has served in Iraq, Belize, Hong Kong and Germany.