Yulia Tsvetkova was arrested in 2019 and charged with distributing pornography after posting drawings of vaginas on social networks as part of a project to question the portrayal of body image in the media.
She was later labelled a foreign agent and spent four months under house arrest, in a move her supporters said was linked to activism and campaigning for feminist issues and lesbian, gay, bisexual, and transgender rights.
Russia's top human rights organisation Memorial recognised Tsvetkova as a political prisoner and called for her release. The case was initiated following a complaint by a hard-line anti-LGBT campaigner, Memorial said.
On Friday, a court in the far eastern city of Komsomolsk-on-Amur acquitted Tsvetkova, a Telegram channel set up by her supporters said. Prosecutors had last month requested she be sentenced to three years in a prison colony.
"The three-year long trial ended with victory for the defence," Tsvetkova's supporters said on social media. "We are happy, but not completely yet. The prosecutor's office has 10 days to appeal."
It is a rare reprieve for a Russian activist in a country where more than 99% of all cases that make it to court end in a conviction.
Supported by the ultra-conservative Russian Orthodox Church, Russian President Vladimir Putin has passed multiple laws over the last decade to restrict LGBT rights and assert what he calls "traditional values".
Russian lawmakers this week proposed to extend the country's "gay propaganda" law - which bans the portrayal of "non-traditional" relationships to children - to cover adults as well.
The law has been used to stop gay pride marches and detain LGBT activists, and rights groups say it has been applied broadly to intimidate Russia's LGBT community.