The tenacious Argentine comfortably defeated Fernando Verdasco 6-2 6-3 to capture silverware for the first time on South American soil.
Schwartzman sank to his knees after converting his first match-point – and he will enter the Top 20 for the first time on Monday.
The 25-year-old is now a two-time ATP champion – after triumphing in Istanbul in 2016 – and he is the first Argentine to depart the Rio Open unbeaten.
Verdasco, who joined forces with his compatriot David Marrero to win the men’s doubles event on Saturday, looked to be in discomfort throughout the final. The 34-year-old was often spotted limping and grimacing between points, and his challenge failed to ignite.
The Spaniard made an imposing start and achieved a break of serve in the first game of the contest. His formidable forehand inflicted significant damage as he established an early lead, however his level of play soon plummeted.
Verdasco committed four unforced-errors in a mistake-ridden game to gift his rival parity on the scoreboard, and he continued to miscue for the remainder of the set.
The industrious Schwartzman capitalised on his opponent’s woe and claimed five of the next six games to move halfway towards his target.
The second set was much more competitive. The games were often punishing and protracted, but the majority of lung-busting exchanges went the way of the younger man.
The Argentine frustrated his opponent with his impressive defensive skills, and unlike his vastly-experienced rival, he made the most of his opportunities. Verdasco created nine break-point chances in the match, but made just a single breakthrough.
The Spaniard nudged a forehand beyond the baseline to slip 4-2 behind, and he failed to claw his way back into contention. His frequent use of the dropshot in the closing stages – without great success – further highlighted his physical difficulties.
It was also a day to remember for Frances Tiafoe. The likeable American, a wildcard entry, eased to his first ever ATP title in Delray Beach after a convincing 6-1 6-4 victory over Peter Gojowczyk in a 61-minute final.
“I just can't believe it,” beamed Tiafoe, who defeated Juan Martin del Potro en route to his unexpected triumph.
“A lot's going through my mind. If you had asked me 10 years ago if I was going to win a title at 20 years old, I probably would have laughed. It's unbelievable.”
In Marseille, there was delight for another promising youngster with a big future. Karen Khachanov edged out home-favourite, Lucas Pouille, 7-5 3-6 7-5 to net the Open 13 title.
It’s the second time the Russian has been victorious at main-tour level, and he was delighted to round off a productive week on the right note. “I am extremely happy, but I just need to keep working and keep going,” said Khachanov.
“I felt I was playing good here from the first day. It's nice to play on a full court in the final, and I hope to come back next year.”