The regional court in the southwestern city of Mannheim found presenter Jörg Kachelmann, 52, not guilty of sexually assaulting his partner at knife-point after an argument.
Presiding judge Michael Seidling said as he read out the verdict to applause from the packed courtroom that the prosecution had failed to make its case beyond a reasonable doubt during the eight-month-long trial.
"None of the evidence is in itself sufficient to prove the guilt or even the innocence of the accused," he said, as Kachelmann listened impassively.
Seidling added that Kachelmann was entitled to compensation for the four months he spent in pretrial detention as well as his legal costs.
Prosecutors said they were weighing whether to appeal.
Kachelmann was popular throughout the German-speaking world for his rollicking weather reports on public broadcaster ARD before his shock arrest last year.
The accuser, a now 38-year-old radio presenter with whom he had an on-again, off-again relationship for 13 years, had alleged that Kachelmann attacked her in her apartment after a dispute over another woman.
She testified that he held a kitchen knife with an eight-centimetre (three-inch) blade to her throat and raped her.
But doubts soon surfaced about her account, along with allegations that prosecutors had ignored exculpatory evidence while building their case.
Critics said the blanket media coverage of the accusations against Kachelmann as well his affairs with several other women had destroyed his career before a verdict could be delivered.
Meanwhile women's rights groups said the intense scrutiny of the accuser in the press would keep victims of sexual assault from going to the police.
Judge Seidling noted that the trial had left its mark on both sides.
"We are dismissing both the accused and the accuser with a suspicion that can perhaps never be lifted – he as a potential rapist, and she as a potential vengeful liar," he said.
Justice Minister Sabine Leutheusser-Schnarrenberger was also strongly critical of the attention given to the case.
She said the presumption of innocence was "in danger if the media deliver their verdict long before the judges have spoken," in an interview with the daily Passauer Neue Presse.
The burly Kachelmann with a lilting Swiss accent had been a fixture on ARD newscasts since 2002 and had a major following for his fanciful descriptions of precipitation, clouds and the jet stream.
He became an Internet phenomenon two years ago when a large tabby cat wandered onto the set during a broadcast and he scooped it into his arms and continued his report. The clip drew more than 1.1 million hits on YouTube.
The alleged rape occurred just before Kachelmann left to help cover the Winter Olympics in Vancouver. He was arrested at Frankfurt airport upon his return from Canada.
ARD said it would decide whether to put Kachelmann back on the air pending an appeal when the verdict is final.