Having already won two stages of the race, Hermans finished comfortably in the peloton on the sixth and final stage, which took the riders 152km from the picturesque The Wave Muscat to Corniche Mutrah.
Alexander Kristoff, meanwhile, claimed the stage win in style, holding off Romanian Eduard Grosu and Italy's Sacha Modolo to earn his third victory of this year's race.
This year's race, the eighth edition of the Tour of Oman, was without several high-profile riders, including past winners Chris Froome and Vincenzo Nibali.
After winning in Oman in 2013, Froome emerged victorious that year in the Tour de France, while a year ago Nibali took the Giro d'Italia after victory in the Tour of Oman's seventh edition.
After grabbing the overall lead after stage two, few expected Hermans to maintain his advantage on stage five -- the grueling mountain finish named 'Green Mountain.'
But the 30-year-old held off the advances of his nearest competitor -- Portuguese Rui Costa -- to take an unexpected win.
That victory allowed Hermans to coast through to the line in the chasing pack in Sunday's final stage, finishing 22 seconds ahead of Costa in the overall classification.
"Amazing race, landscapes and challenging stages," Hermans wrote on his Instagram feed.
More accustomed to playing second fiddle to Philippe Gilbert at Team BMC, Hermans was given his chance at center stage after the Frenchman moved to Quick Step.
Hermans has certainly made the most of what he calls a "newfound responsibility and freedom" at BMC, which also includes a runner-up spot in last month's Tour of Valencia.
"To be worthy of this confidence I worked really hard over the winter, that's clearly the reason behind my early season form," Hermans told reporters after stepping off the podium.
"The aim now will be to build on this in the Ardennes classics," he added, referring to the Amstel Gold Race, La Flèche Wallonne and Liege-Bastogne-Liege, which are held in April.
Vuelta a Andalucia
Meanwhile in Europe, Spain's Alejandro Valverde won the Vuelta a Andalucia for the fifth time in six years, holding off illustrious compatriot Alberto Contador in an intriguing finale to win by only a second.
In conditions that belied the race's Ruta del Sol (Route of the Sun) monicker, former Tour de France winner Contador was unable to break free and create the two second gap he needed to win.
Valverde and Contador both crossed the line in the driving rain bunched up in the peloton, 1 minute 45 seconds behind final stage winner Tim Wellens.
Valverde adds the 2017 title to the wins he picked up in 2012, 2013, 2014 and 2016, with Froome the only rider able to break his recent monopoly of the vuelta in recent years -- though the Spaniard didn't compete in 2015.