Denmark until now was the only country that had not issued a permit for the pipeline, a controversial project which is opposed by Poland.
Nord Stream 2 is also to run through waters belonging to Russia, Finland, Sweden and Germany.
Warsaw has strongly criticised the project amid concerns that the pipeline will make the European Union more dependent on Russian gas.
The 1,200-kilometre link is expected to have the capacity to send around 55 billion cubic metres of Russian natural gas a year to Germany under the Baltic Sea, while bypassing the Baltic states, Poland and Ukraine.
US President Donald Trump in June warned Berlin against the project, saying it “really makes Germany a hostage of Russia if things ever happen that were bad.”
US Vice President Mike Pence warned earlier this year that America “cannot ensure the defence of the West” if its allies grow dependent on Moscow as a result of projects such as Nord Stream 2.
Polish Prime Minister Mateusz Morawiecki said in May 2018 that Nord Stream 2 was “a new hybrid weapon” aimed at the European Union and NATO.