The 43-year-old managed to make his way around a rock-hard Emirates Golf Club in two-under par 70 to finish on 17-under-par 271 for the tournament.
South African Brandon Stone (72) finished in second at 13-under par as Scotland’s Robert MacIntyre paid the price of four successive bogeys around the turn for a 74 and solo third place at 12-under par 276.
England’s Laurie Canter (72) closed with back-to-back birdies to tie for fourth at 10-under par with Finland’s Kalle Samooja (71).
It was Casey’s 15th title on the European Tour, but the first since the 2019 European Open.
Currently ranked 27th in the world, he is expected to improve to number 14 when the new rankings are released on Monday.
Casey made a birdie on the par-5 third hole, and then chipped-in from a horrible lie on the par-3 fourth for an unlikely birdie.
And even though he made three bogeys after that as the firm and fast greens played havoc with the scores, he compensated well with three birdies, including one on the last hole.
The European Tour moves to Saudi Arabia for the Saudi International next week, and Casey is part of the field there.