Switzerland can take part in the international Thermonuclear Experimental Reactor Organisation (ITER) project in France.
Tuesday's vote by the House of Representatives comes after the Senate gave its full backing to the initiative in September.
ITER was established on October 24, 2007. Seven members are engaged in the project: China, the European Union, India, Japan, Korea, Russia and the United States, with the costs being shared among them.
Switzerland has been closely involved in the ITER project and contributes financially to European nuclear fusion within the framework of its support to the EU's seventh research programme (2007-2013), which amounts to SFr8 million ($6.8 million) a year.
On Tuesday the government said ITER would be by far the most important element of European nuclear research and therefore Switzerland wanted to be closely involved.
The principal goal of ITER is to generate 500 megawatts of fusion power for periods of 300 to 500 seconds with an input power of 50 megawatts.
ITER is being built in Cadarache, southern France on a 180-hectare site. The experimental reactor will be 60 metres tall and weigh as much as an aircraft carrier. Some 300 people currently work for ITER at Cadarache with 2,000 more researchers based around the world.
The demonstration reactor is expected to be operational in 2018. A commercial reactor is not expected before 2040.