Reed started the final round on the Majlis course of Emirates Golf Club four shots clear of second-placed David Puig of Spain, and shot an even-par 72 with two birdies and two bogeys.
That was good enough for a massive win for the American, as the best score among those finishing in the top-18 was three-under par 69.
Englishman Andy Sullivan fired a final round 71 to take second with Frenchman Julien Guerrier one stroke further back in third.
Puig's 75, which included a two-shot penalty for grounding a club in the bunker at the last, saw him slip down the leader board as he finished seven under.
Reed becomes the sixth American winner of the Dubai Desert Classic with victory set to move him to No.2 in the Race to Dubai Rankings, and up 18 places to 26th in the official world rankings.