The court in Aix-en-Provence gave activist Cedric Herrou a four-month suspended sentence -- half the length the prosecutor had asked for, but more than his initial sentence.
"This is a warning sentence," the court's senior judge told him. "If you are convicted again, you risk having this sentence applied."
Herrou was unrepentant as he emerged from court, where around 30 activists and supporters were on hand to support him.
"They'll just have to put me in prison, it'll be simpler," he said. "I will continue to fight from prison."
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Cedric Herrou. AFP
He would be appealing the sentence to the country's top court, he added.
Earlier, just before entering court to receive his sentence, he told reporters: "It is the role of a citizen in a democracy to take action when the state fails to."
Herrou, an organic olive farmer, is a leading figure in Roya Citoyenne, an association dedicated to helping migrants.
At his original trial in February, he received a suspended 3,000-euro fine for helping migrants on the Italian side of the border cross the border.
But he was acquitted on another charge of sheltering around 50 Eritrean illegal migrants at a disused railway building.
The appeals court Tuesday confirmed the first conviction but reversed the acquittal.
Hailed as a hero by some, irresponsible by others, Herrou was in no mood to compromise Tuesday.
"I say to all the families I helped that I do not regret anything, that I did it with pleasure," he said.
"If the immigration was coming from the north of Europe, the courts wouldn't be acting this way, this is state racism," he added.
Herrou is one of several people to appear in court in southern France charged with illegally assisting migrants who have travelled up through Europe after crossing the Mediterranean in rickety boats.
His home is just a few kilometres from the border with Italy and despite the court case he continues to help migrants who turn up on his doorstep prepare their applications for asylum.
Last month he was arrested and charged as he accompanied 156 migrants to Marseille to help them file their asylum requests.
Since the beginning of 2017, more than 117,000 people have made the perilous Mediterranean crossing into Europe from north Africa -- more than 96,000 of them arriving in Italy.
Already this year, 2,417 had died attempting the crossing, according to figures from the UN refugee agency (UNHCR).