Judge Susanne Hemmerich said there was not enough evidence to back the accusation the 2014 World Cup winner was a "notorious woman beater".
She imposed a warning and a conditional fine of 200,000 euros ($217,709) which is only payable in case of any new convictions.
Boateng's former partner and mother of his twins had accused him of assaulting and insulting her during a Caribbean holiday in 2018.
Boateng, now 35, was convicted in 2021 and fined 1.8 million euros in an initial trial, and his appeal to overturn the ruling then was unsuccessful.
But in a third legal try, he won a bid for a retrial as the court agreed with Boateng's legal team that one of its challenges for bias had been unfairly decided.
During the initial trial, Boateng's former partner told the court he had punched her, causing her to lose her breath for a moment during a heated argument.
The alleged incident happened in the weeks after the 2018 World Cup in Russia, when Boateng was in the Germany squad which was knocked out in the group stage.
Boateng's former partner described how he "pressed against my eye with his thumb, bit me in the head and pulled me to the floor by my hair".
She said he repeatedly insulted her and hit her on the back with "one strong punch and several light punches".
Defender Boateng played for German giants Bayern Munich for a decade before signing for France's Lyon in 2021.
He joined Austrian club LASK earlier this month on a two-year deal.
