Pella, who had previously reached four ATP finals and come up short each time, made no mistake against the young Chilean and finished a superb week without dropping a set.
Ranked 48th in the world before his triumph, the 28-year-old will jump to a career best 34th place when the new rankings are published on Monday.
Pella stopped Garin from becoming the first Chilean since Fernando Gonzalez a decade ago to lift an ATP trophy and is the seventh player to claim their first ATP title this season.
The other first time winners are Alex de Minaur (Sydney), Tennys Sandgren (Auckland), Juan Ignacio Londero (Cordoba), Reilly Opelka (New York), Laslo Djere (Rio de Janeiro) and Radu Albot (Delray Beach).
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
(Reporting by Andrew Downie; Editing by Ken Ferris)
