Ferrer had key breaks in each set and defended his own service game well to earn the title at the City of Arts and Sciences. Granollers netted Ferrer's serve to finish the all-Spanish final on the indoor surface.
Ferrer's second win of the season and ninth of his career moved him ahead of Andy Roddick and into seventh place in the points standings. The top eight qualify for this month's season-ending ATP World Tour Finals in London, 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 with his parents. "I'm so happy, there are no words to describe it."
Ferrer, who won here in 2008 when the tournament was a spring clay event, went ahead 5-3 in the first set when he broke Granollers with a passing shot. But the 67th-ranked Granollers, a Barcelona native, responded by breaking right back in the same manner.
Ferrer closed out the first set with another break when his backhand shot touched the far corner as Granollers hesitated.
Ferrer maintained the momentum in the second set, building a 3-0 lead on his way to his 59th victory this season.
Granollers, who gained entry as a lucky loser after Jo-Wilfried Tsonga pulled out to injury, dropped to 1-1 in finals. He captured a tournament in Houston in 2008.
"You deserve this," Granollers said to Ferrer during the trophy ceremony. "You're a great player and you've fought a lot to achieve what you have."