"What I'm doing is not a sacrifice, it's an honour," Herrou, 37, told a crowd of about 300 suppoters before his trial in Nice opened.
Herrou, who farms olivs and eggs in the Roya Valley near the Italian border, is one of three people in the area to appear in court recently for illegally assisting migrants travelling up through Europe after crossing the Mediterranean in unseaworthy boats.
Herrou's is not the only such case
In October a researcher at the University of Nice, Sophia Antipolis, was tried for giving a lift to three Eritrean women shortly after their arrival from Italy.
Prosecutors called for a six-month suspended sentence.
The ruling in her case is expected on Friday.
In December a 73-year-old academic, also living in the area, was fined 1,500 euros for a similar gesture.
Herrou claimed he was picking up the slack for "a state that put borders in place and is absolutely not managing the consequences".
He has been outspoken in his criticism of France's response to the migrant crisis, accusing the police of detaining thousands of minors and dumping them back across the border in Italy.
He is being prosecuted for housing 50 Eritreans in a former holiday camp for employees of the SNCF rail company and their families in October 2016.
Local right-wing politicians slammed the move and police cleared the building after three days.
He was also arrested in August for transporting eight Eritreans but the case was dropped.
Public prosecutor Jean-Michel Prêtre called for Herrou to be given an eight-month suspended term, for his vehicle to be confiscated and for his driving licence to be restricted to driving only for professional use.
He accused Herrou of using the court as a "political platform" to justify his acts.
"We find ourselves in the situation of an intentional trial, the product of a media strategy designed to showcase a cause," Prêtre said. "It's not the job of the judicial system to change law and it's not its job to give lessons in diplomacy to such-and-such a country."
A verdict is to be announced on 10 February.