The fourth seed capped off a remarkable return to the highest level by winning the final 13-11 7-11 5-11 11-5 14-12 in his first competition on the world circuit since the British Open in May.
Ashour, who has struggled with injuries, booked his place in the final at the expense of French world number one Gregory Gaultier, while Elshorbagy saw off 2013 champion Nick Matthew.
In a repeat of the 2012 final, the pair put on an entertaining display, which saw the two trade games early on.
Having shared the opening four, both were guilty of wasting championship-point opportunities in the finale, with the penultimate point going down to a let decision from the officials.
Amid high drama, Ramy sealed his comeback win after 90 minutes on court.
Having ended Elshorbagy's 23-match winning streak, Ashour paid tribute to his opponent and described the achievement of capping his comeback with a third world title.
"I'm speechless, it's unbelievable," he said on court.
"I've worked so hard and pushed myself, you've no idea how hard. To get this as a reward, there's no way this can get any better.
"[Elshorbagy] pushed me to my limits and both of us represented our country in the best manner. It's been crazy."