A panel of three judges dropped all the charges against Rwigara, her mother Adeline and four co-accused.
"All charges... have been dropped. The court finds that the prosecution charges were baseless," the judges said in their ruling.
Rwigara, 37, was arrested in September 2017 after her attempt to run in Rwanda's July presidential election was denied on grounds she had allegedly forged signatures of supporters for her bid.
She was also charged with inciting insurrection for comments criticising the government and President Paul Kagame in the run-up to the election.
The judges ruled that the prosecution failed to prove that Rwigara had personally forged signatures.
The court also ruled that Rwigara's criticism of government through press conferences was freedom of speech which was guaranteed by both the constitution and international law.
The same also applied to her mother, with the court ruling that Whatsapp voice notes she had sent to her relatives accusing the government of ruling through fear amounted to her merely expressing her right of freedom of speech in a private manner.