The plutonium was sent over on the condition that it would be safely destroyed in a cooperative effort to increase worldwide nuclear safety.
"This highly sensitive material has now, under high security ... been transferred to the United States for disposal within the framework of the US Global Threat Reduction Initiative (GTRI)," Bildt wrote in an article published in Swedish daily Dagens Nyheter.
The GTRI is aimed at protecting sensitive material to prevent it being used for the production of nuclear devices or in acts of terrorism.
The plutonium, which Bildt wrote was shipped to the US “for final and safe disposal”, was allegedly shipped with utmost discretion from the shores of Sweden.
The US government has guaranteed that the plutonium will not be used by the military.
Bildt pointed to this cooperation as being a “concrete contribution” by Sweden in the efforts to prevent the spread of nuclear material.
The Swedish consignment was shipped by boat "under great discretion," Bildt said.
"Several countries have previously shipped enriched uranium, but the Swedish contribution breaks new ground because it is the first time that reprocessed plutonium has been transferred within the framework of the GTRI," he added.
He wrote that the plutonium has its background in Swedish research and development programmes from the 1950s and 1960s.
Most of it comes from the now-closed Ågesta nuclear reactor outside stockholm, while smaller amounts were acquired "at an early stage" from the United States and Britain for research into nuclear weapons.
According to the minister, Sweden's actions can serve as support and inspiration to other countries, and will hopefully lead to an international cooperation in terms of ridding the world of nuclear material.
“Together, we must do all we can to reduce the number of nuclear weapons in the world, to prevent the further spreading and so that they never, ever, shall be used,” Bildt wrote in DN.
On Tuesday, Bildt will discuss this international cooperation at a summit on nuclear safety in Seoul, South Korea.