The state of Qatar has bought 10 per cent of Porsche SE, plus the options that Porsche held on 20 per cent of VW shares.
No announcement was made on how much Qatar paid, or what its eventual holding in the companies could be.
Dr Wolfgang Porsche said: "Today is a historic day for us. For the first time in Porsche's history, an external investor has acquired a holding of ordinary shares that so far have been solely owned by the family members of Porsche and Piech.
"This will not only improve Porsche's liquidity situation, but it is also an important step on the pre-destined road to an integrated automobile company, which we intend to forge together with Volkswagen."
Qatar prime minister Sheik Hamad ibn Jassim ibn Jabir Al-Thani emphasised that the emirate was planning a long-term involvement with Porsche.
"Through our trust-based collaboration with the family shareholders, we will help ensure that the success story of Porsche, and, in the future, of Volkswagen continues to be written," he said.