"By the end of this year, we'll have outfitted 231 of our 255 ICE trains with the necessary technology," DB CEO Rüdiger Grube told the Süddeutsche Zeitung (SZ).
Until now, free wireless internet was only promised to first class passengers, but now Grube says it will be available to all classes starting in 2016.
The upgrade is part of a €200 million investment DB is making to improving passenger services on its long-distance trains, including refurbishing the dining cars.
"(Rail travel) must, simply put, be more comfortable," Grube told the newspaper.
Grube said that the wi-fi will only be enabled when the network has the necessary capacity to handle traffic from all passengers. An ICE can carry as many as 900 passengers.
"If only half of the passengers connect to the wifi, the route has to be so well outfitted that 450 people can rely on one router that connects from one transmitter to another at a speed of 250 kilometres an hour without seeing their connection disrupted," the CEO said of the logistical challenges.
Starting in 2015, DB will release its train-wide intranet service, allowing passengers to download podcasts, movies and games while travelling.
Currently, passengers can connect to a t-mobile Hotspot while travelling at a cost of €4.95 a day.