The Bayern Munich-bound striker scored in either half to secure the honour of being the Bundesliga's top scorer this season as Jurgen Klopp's men received a timely boost ahead of their Berlin showdown against the champions next week.
Lewandowski opened the scoring in the capital on Saturday and Milos Jojic's superb effort put Dortmund 2-0 up before the interval.
A stunning free-kick from Lewandowski nine minutes from time put Dortmund firmly in command and Henrikh Mkhitaryan added the gloss to give them a measure of revenge against a Hertha side who claimed a 2-1 win at Signal Iduna Park in December.
Adrian Ramos was on target for Hertha that day, but the forward was left on the bench until the last 25 minutes for the hosts, scuppering his chances of finishing as the division's leading scorer.
The 16-goal Colombian was said to be suffering from a cold but the decision may have highlighted the home side's reluctance to play the 28-year-old against his future employers.
Klopp's side survived an early scare as Marcel N'Djeng's fifth-minute corner was met by the head of Sandro Wagner, whose effort was blocked on the line by Nuri Sahin.
Roared on by a huge following, the visitors enjoyed prolonged spells in possession but struggled to create clear-cut chances in the opening 20 minutes.
Marco Reus, whose future is the subject of intense speculation, wasted an opportunity to threaten from a long-distance free-kick, his floated delivery proving easy for the home defence to deal with.
Dortmund were assured of second spot before kick-off at the end of a campaign in which they have fallen well short of Bayern, who secured the title in record-breaking time.
But they appeared determined to finish the league season with a bang and Lewandowski put them ahead after collecting a precise pass from Mats Hummels four minutes before half-time.
Jojic struck just three minutes later, cutting inside John Brooks before lifting an excellent left-footed effort beyond Thomas Kraft.
The game could have been put beyond Hertha's reach in the first minute of the second half as Reus fired over from an acute angle after being picked out by Lewandowski.
Jos Luhukay introduced Ramos from the bench in place of the Levan Kobiashvili, who was given a rousing ovation to bring the curtain down on his Hertha career.
Ramos' powerful header from a corner was brilliantly kept out by Roman Weidenfeller in the 68th minute as the hosts' search for a goal continued.
Dortmund saw Reus limp off just a minute later, a worrying sign for both club and country, with the Germany forward replaced by Pierre-Emerick Aubameyang.
But they shrugged off that setback to score twice in the last 10 minutes, Lewandowski looping a stunning set-piece into the top corner for his 20th league goal of the season before Mkhitaryan's scrambled effort capped a dominant display.
