Fujitsu had held an option to buy all of the nine-year-old venture known as Fujitsu Siemens Computer (FSC), and the transaction should be finalised by April 2009, the Japanese company said.
"We will inherit a very solid client base and research and development capacity to underpin the global expansion of our product line," Fujitsu President Kuniaki Nozoe told a news conference in Tokyo.
"This is our first step toward real globalisation. From now on, we will be pressed by customers to show Fujitsu can offer high-value added services and products without the Siemens brand," he added.
Siemens financial director Joe Kaeser was quoted as saying: "We are very happy that our partner is buying our shares. We will continue to refocus our activities on the strategic sectors of energy, industrial equipment and health care."
Asked if Fujitsu was considering new partners overseas, Nozoe said: "Of course, we need an alliance. I cannot tell you details, but we are about to begin such discussions."
He added that "we have not thought about any lay-offs (job cuts)" and that there had been no discussions regarding a mooted sale of the PC business to the Chinese group Lenovo.
FSC had €6.6 billion in sales in its latest fiscal year which ended in March 2008, but faces stiff competition from US rivals Dell and Hewlett-Packard. FSC, which also makes mainframe computers and servers, posted a net profit of €69 million, and operating profit of €72 million.