The new services between Krefeld, Cologne, Bonn, Wuppertal and Münster will start in December 2015 and run for 15 years.
The contract represents part of a larger programme of liberalizing the EU's rail and transport networks. It is expected that around 35 contracts of a similar volume are likely to follow in the next five years.
It will be signed by Tobias Richter, managing director of National Express in Germany, and three representatives from regional German rail services, in the western town of Wuppertal. British Ambassador Simon McDonald will also attend.
Ambassador McDonald called the contract a "vote of confidence from our German partners and a testimony to the strength of British transport companies". "This is a proud day for British business," he said.
National Express' move into German rail transport leads on from its success in the UK's newly- coach market.
While several European companies have negotiated transport contracts in the UK, British transport providers have thus far had trouble breaking into the continental market.
Richter said his company was "delighted" to have been awarded the contracts, saying that as the "operator of the UK's best performing rail franchise", National Express would focus on delivering North Rhine Westphalia's 18 million people "services of the highest quality".
Figures released in June this year show National Express trains in the UK recording a yearly average of 97.3 percent of trains arriving on time, compared to a national average of 91 percent.
Richter will be aiming to provide the same punctual service to efficiency-conscious German customers. "We cannot wait to get started", he said.
But National Express has also seen its share of controversy. In 2009, the firm had its franchise on the UK East Coast main line rail services terminated three years early because it could no longer afford to operate the services.
National Express had run the franchise, which ran services between London and the east of England since 2007.
-Deutsche Bahn announced on Tuesday that passengers at 105 train stations will now be able to get free wi-fi for 30 minutes in a deal with Deutsche Telekom. Customers will be logged out after 30 minutes and will then have the option of paying.
Alex Evans/ The Local