Maria Ponomarenko is being sentenced for having written critical posts on social media about the attack on a theater in the Ukrainian city of Mariupol last March.
The bombing, which Russia blamed and has denied, made world news and was condemned by Ukraine.
For a long time it was uncertain what had happened.
According to Mariupol's mayor, over 1,000 people were in the building when it was attacked.
Ukrainian authorities estimated that around 300 people who sought refuge in the theater lost their lives in the attack, but according to an analysis by the news agency AP, more than 600 people must have died.
Russian authorities began pursuing Maria Ponomarenko in 2020, following her revelations about corruption.
She wrote about local politicians denying housing to orphaned children to which they were entitled.
Then Ponomarenko's family began to receive threats and eventually left the city.
For years, Ponomarenko participated in anti-regime protests, according to Meduza - an independent Russian news site.
One of several who are sentenced
Ponomarenko's case is the latest in a row since Russia introduced a new law last March.
According to the law, people found guilty of "deliberately spreading false information about Russia's armed forces in Ukraine" can be fined or imprisoned for between five and ten years.
May not work as a journalist
Maria Ponomarenko's trial was held in the city of Barnaul in Siberia, where she worked for the RusNews website.
The court also ruled that Ponomarenko is banned from working as a journalist and participating in digital events for the next five years, according to several media citing her lawyer Dmitry Shitov.
Prosecutors had asked for a nine-year prison sentence.
Watch Maria Ponomarenko's speech before the court before the verdict was handed down, in the clip above.