Harry, 21, third in line to the throne, has opted to join the Blues and Royals regiment of the Household Cavalry, his father Prince Charles's Clarence House residence said Wednesday.
The Household Cavalry are expected to be deployed to Iraq in the future.
Harry is due to complete his officer training at Britain's elite Sandhurst military college in April. He will become a second lieutenant in the cavalry once commissioned as an officer.
A Ministry of Defence spokesman said: "It's fair to say that if his squadron goes to Iraq, he will probably go with it."
The prince could see front-line action if officials allow him to take part.
A Clarence House spokesman said: "He based his decision on the variety of roles which the regiment undertakes, including reconnaissance support to airborne forces right through to ceremonial duties."
Harry hopes to become an armoured reconnaissance troop leader at the forefront of army operations.
In an interview to mark his 21st birthday in September, Harry insisted he would be willing to serve on the front line once his training days as Officer Cadet Wales are over.
"There's no way I'm going to put myself through Sandhurst and then sit on my arse back home while my boys are out fighting for their country.
"That may sound very patriotic, but it's true. It's not the way anyone should really work."
The last British royal to see military action was Harry's uncle Prince Andrew, who flew as a helicopter pilot in the Falklands War in 1982.