The Swede, who is new to Formula E this season, saw off a challenge from Lucas di Grassi to clinch the first of two races being held in the German capital this weekend.
It was also a momentous day for his Mahindra Racing team who hadn't registered a win during its three seasons in the all-electric race series.
Di Grassi had sprinted to pole earlier in the day, pipping DS Virgin Racing's Jose Maria Lopez by 1,000th of a second, but could do nothing to repel Rosenqvist as the race progressed.
The 25-year-old rookie had started from third but immediately jumped a place as Lopez got a sluggish start.
Relentless in his pursuit of the more experienced di Grassi, Rosenqvist seized his opportunity on lap 22 of the 44-lap race taking the lead before he and di Grassi pitted to swap cars -- Formula E drivers use two cars during a race.
It was a decisive move and from then on in Rosenqvist controlled the race as di Grassi struggled with battery power problems.
"Finally we got it -- it's been a long time," Rosenqvist told CNN. "It felt like we could win many races this year but it was a day when all the puzzle pieces came together.
"Even with some small mistakes we were still able to get the win ... just fantastic for everyone, for the team," he added.
"We work so hard and you can really see the suffering sometimes but when you have days like this it's all worth it."
Di Grassi, meanwhile, was satisfied with his day's work, given the issues with his car -- the Brazilian was also nursing a sore ankle after injuring it during a football match earlier in the week.
"It was a good day -- pole and second place," di Grassi said. "With the battery we had a lot of temperature problems ... we are gonna improve the car, make sure the car is better (tomorrow) and fight for the win."
Di Grassi was followed home by Rosenqvist's Mahindra teammate Nick Heidfeld, while championship leader Sebastien Buemi clawed his way back into the points after starting from 14th on the grid but was later disqualified for a tire pressure infringement.
The result means that di Grassi closes the gap to 22 points on Buemi at the top of the driver standings -- the Swiss now has 132 points to the Brazilian's 110.
Rosenqvist's win moves him up to fourth with 65 points, three points behind Buemi's Renault eDams teammate Nico Prost.
The drivers will be back on track on Sunday for the second race of the double-header.