The Renault team posted a teasing picture on Twitter of the 32-year-old removing his helmet after driving the 2012 Lotus E20 car at Valencia's Ricardo Tormo circuit.
"So guys...we need to come clean about something," the caption said.
"It's true. It really is Robert Kubica," the team added in a later post. "Back in one of our cars after six years."
The test took place amid considerable secrecy, with no advance notice given to the media and little information provided about the reasons for the private test.
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"So why did we keep it quiet? It was a private test, for Robert," the team said, adding that the Pole had completed 115 laps with "the biggest smile" afterwards.
Kubica, who in 2008 became the first Pole to win a Formula One race when he triumphed with BMW-Sauber in Canada, last drove a Formula One car with Renault in pre-season testing at the same circuit in February 2011.
Renault have left and returned to the sport with their own team since then, with a current line-up of Germany's Nico Hulkenberg and Britain's Jolyon Palmer.
The latter has yet to score a point in six races this season with increasing media speculation about his future ahead of this weekend's Canadian Grand Prix.
Kubica's F1 career ended in the same month as his last test when he suffered severe arm, leg and hand injuries in a near-fatal crash during a minor rally in northern Italy that he had entered for fun.
He had been one of the sport's brightest prospects before his accident, with a likely move to Ferrari on the horizon.
Since his recovery he has competed in the world rally championship and tested other cars, including those used in Formula E and GP3.
(Reporting by Alan Baldwin, editing by Toby Davis)
