Gorbachev is getting involved in a high-profile case
The plea came in an open letter published on Mr Gorbachev's website.
Prosecutors in Russia accuse Alexander Ponosov of running pirated software on school computers, violating intellectual property rights.
Russian President Vladimir Putin has also criticised the prosecution of Mr Ponosov, in Perm, east of Moscow.
Mr Gorbachev's letter, on the website run by his charitable foundation, said "many people in Russia regard this scandalous case as trumped-up, launched on the initiative of Microsoft corporation to set a precedent".
'Show mercy'
"We have great respect for the work of Microsoft's programmers... and are in no way casting doubt on the principle of punishment for intellectual property violations.
"However, in this case we ask you to show mercy and withdraw your complaint against Alexander Ponosov," the letter read. It was also signed by Russian parliament deputy and banker Alexander Lebedev.
Mr Gorbachev said that under Russian criminal law the teacher could face "imprisonment in Siberian camps".
The Perm region lies in the Ural Mountains, between Moscow and Siberia.
The teacher is accused of knowingly using pirated Windows software in the school and causing the company losses put at 266,000 roubles ($10,000; £5,000).
Mr Ponosov told the BBC that Russian prosecutors had brought the case against him and he was unaware of any Microsoft claim against him.
He says he is innocent, that the software had been pre-installed and he did not know it was unlicensed when he obtained the computers.
At a news conference on 1 February, President Putin said investigators should "go after the distributors, not the users".
"It's ridiculous to just arrest a chap for using computers," he said.
La firme '''Microsoft''' a décidé de poursuivre, en Russie, un enseignant pour usage de copies pirates d'un logiciel Microsoft sur les ordinateurs de son école. Le professeur, M. Alexander Ponosov, a plaidé non coupable et indiqué qu'il avait légalement acheté l'ordinateur sur lequel était installé le logiciel en question, qu'il ne savait pas avoir été piraté.
 
Le Président russe, '''Vladimir Poutine''', a critiqué la procédure lancée par Microsoft contre l'enseignant : .

L'ancien chef soviétique, '''Mikhail Gorbatchev''', a aussi pressé Microsoft d'abandonner les poursuites, demandant l'indulgence de la compagnie pour l'enseignant et a ajouté que ce professeur, s'il était jugé coupable, .

Selon M. Gorbatchev,