"Chairman of the Management Committee Alexei Miller said that this morning at 8.45 Moscow time (05:45 GMT) construction of the Nord Stream 2 gas pipeline was fully completed," Gazprom said in a statement.
Nord Stream 2 has divided European capitals and raised tensions between the bloc and Washington.
A key controversy is that it diverts supplies from an existing route through Ukraine and is expected to deprive Europe's ally of annual transit from Russia.
Running from Russia's Baltic coast to northeastern Germany, the underwater, 1,200-kilometre (745-mile) pipeline follows the same route as Nord Stream 1, which was completed over a decade ago.
