Victors on their previous two Bundesliga visits to Berlin, Hannover made it three wins in a row to move up to fourth in the table ahead of the weekend's action.
Jimmy Briand opened the scoring a minute before half-time and Tayfun Korkut's men had several opportunities to extend their advantage before Hiroshi Kiyotake wrapped up the points late on.
Hertha have now lost six of their 11 league games this term and head into the international break on the back of successive defeats, while Hannover have won three matches in succession.
The visitors moved ahead when Briand met a right-wing corner with a sweetly struck half-volley that flashed past Thomas Kraft.
Leonardo Bittencourt came close to rounding off a fine Hannover move early in the second half, while Kiyotake had a goal chalked off for offside.
However, those two players then combined to put the game beyond the hosts.
After Marvin Plattenhardt had failed to control a pass, Hannover broke quickly and Bittencourt switched the play right to find Kiyotake, who cut back on to his left foot before finding the net.
