She told Swedish media that she will not be appealing the verdict.
Climate activist Greta Thunberg has been found guilty by a Swedish court of disobeying a police order at a protest in Malmo last month.
The 20-year-old avoided a potential prison sentence and has been fined 2,500 Swedish krona (€216), AFP reports.
Greta had pleaded not guilty and told the court: "My actions are justifiable," according to the Sydsvenskan newspaper.
"We are definitely not going to back down because of this,” she told reporters after the verdict.
“We don't have any laws that long term protect us against the self-destructing greed that we have let [have] full control over the world. The laws have to be changed. We know that we cannot save the world by playing by the rules because the rules have to be changed."
Irma Kjellström, spokesperson for Ta tillbaka framtiden (Take Back the Future), the group involved in the protest, said: “It's even more clear than it would have been otherwise that we have to be exactly where the harm is being done, that we have to be out in the oil ports defending our lives, because apparently currently the states and other power actors are not ready to do what's needed."
What was the verdict in Greta Thunberg trial?
Greta was charged because she refused to comply with police orders to leave the scene during the protest, according to Swedish Prosecution Authority spokeswoman Annika Collin and a statement from prosecutors.
Greta inspired a global youth movement demanding stronger efforts to fight climate change after staging weekly protests outside the Swedish Parliament starting in 2018.
What happened at the Malmo climate protest?
Starting on 15 June, climate activists staged a multi-day protest at Malmö's port.
Led by youth group Take Back the Future, protestors physically blocked oil tankers in the harbour.
"The climate crisis is already a matter of life and death for countless people," Greta tweeted during the protest. "We choose to not be bystanders, and instead physically stop the fossil fuel infrastructure. We are reclaiming the future."
When the protestors were ordered to move to allow vehicles to pass, Greta was among those who refused. She was then dragged away by police.
Earlier in the year, the climate activist was briefly detained by police in Oslo during a protest against wind farms built on Indigenous land in Norway.