The verdict, announced by the governing International Automobile Federation (FIA) in a statement after a seven-hour hearing in Paris on Thursday, was accepted with relief by the team led by Formula One veteran Ross Brawn.
"Mercedes accepts the proportionate penalties of a reprimand and suspension from the forthcoming young driver test," they said in a statement, adding that they would not appeal.
The tribunal had the power to impose a heavy fine, dock points or even ban Mercedes from the world championship - although that was never a likely option for one of the sport's major players who are currently third overall.
Champions Red Bull, who had protested to the FIA at last month's Monaco Grand Prix when they found out Mercedes had used their current car and drivers in the test, had indicated they wanted to see a tough response.
The tribunal ruled in its detailed written verdict that Mercedes had not intended to obtain any unfair sporting advantage by taking part in a tyre test in Barcelona.
"Neither Pirelli nor Mercedes acted in bad faith at any material time," the tribunal said, declaring that both parties had disclosed to the FIA 'at least the essence' of what they intended to do and had sought permission.
Both Mercedes and Pirelli had said the test was private, not secret, and denied accusations the team had gained an unfair advantage from it.