Ferrer used key breaks in each set and defended his own service game well at the City of Arts and Sciences. Granollers netted Ferrer's serve to secure the win in the first all-Spanish final on an indoor surface since 2000.
Ferrer's second win of the season - and ninth of his career - moved him ahead of Andy Roddick into seventh place in the points standings to virtually secure his place in the season-ending tournament in London later this month. The top eight qualify with only the Paris Masters left to play.
"This is one of the of the happiest days of my career, if not the most," an emotional Ferrer said after climbing into the stands to celebrate a victory at his home event with his parents."I'm so happy, there are no words to describe it."
Granollers played aggressively to save four break points in the sixth game after both players held serve to start.
The Barcelona native - ranked 67th - saved the first through impressive serve-and-volley play before making it 3-3 after saving the fourth with a drop shot.
Ferrer, who won here in 2008 when the tournament was a spring clay event, finally got ahead 5-3 after breaking his opponent with a passing shot. But Granollers eliminated that advantage by breaking right back in the same manner.
Ferrer clinched it on his first set chance as he slapped a backhand shot that managed to touch the far corner as Granollers hesitated to be broken for the second time.
Ferrer maintained the momentum in the second set as he hit a crosscourt passing shot for his third break point. He then held off Granollers in a spirited rally in the next game - finally winning it on his fourth advantage - to hold serve for 3-0 on his way to his 59th match victory this season.
Granollers, who gained entry as a lucky loser after Jo-Wilfried Tsonga pulled out with an injury, dropped to 1-1 in finals after reaching a final for the first time since his win in Houston in 2008.
"You deserve this," Granollers said to Ferrer during the prize ceremony. "You're a great player and you've fought a lot to achieve what you have."