On-field umpires Billy Bowden and Simon Taufel, and TV umpire Asad Rauf reported Ahmed for a second time under ICCbowling regulations during the first Test against England at Multan last month.
"An independent assessment by the University of Western Australia confirmed that he bowled with an illegal action," the ICC said.
Under ICC regulations, a bowler can straighten his arm by 15 degrees at the time of delivery. If he exceeds that, his action is liable to be questioned.
"Given Mr Ahmed's current level of maximum elbow flexion ... he probably bowls some deliveries in each innings that are above the acceptable 5 degrees tolerance limit," Professor Bruce Elliott, a biomechanic at the university said in a report on the Pakistani bowler' technique.
The assessment of Ahmed's ation was based on footage from the Multan Test and compared with a University of Western Australia laboratory assessment that he underwent in September.
Ahmed, the first bowler to be banned for 12 months, can appeal to the ICC's specialist Bowling Review Group to try to overturn the ban. He must lodge a request for such a hearing within 14 days.