Pierre le Guennec, now in his 70s and retired, says the world-famous artist and his wife Jacqueline gave him the oil canvases, drawings and Cubist collages when he was doing work on the last property they lived in before Picasso died in 1973.
But some of the artist's heirs, including his son Claude, suspect otherwise and filed a complaint against the couple, who were charged in 2011.
The trial in the southeastern city of Grasse, which is likely to be closely scrutinised by the art world, was expected to last three days.
Claude Picasso, who runs the Picasso Administration which authenticates the art legend's works of art, is one of the plaintiffs in the case.
Others include Paloma, Claude's sister, another child Maya, two grandchildren and Catherine Hutin-Blay, the daughter of Picasso's last wife Jacqueline.
The former electrician says that when he was working on Picasso's home in Mougins, an upmarket town in the hills outside Cannes on the French Riviera, the artist often invited him to have some cake and drink coffee.
"We talked about everything and nothing," he told AFP in 2010.
"One evening when I left work, Madame gave me a small packet and said 'this is for you'," he said.
"When I came home, I saw sketches, pencil drawings. I didn't know anything about all this.
"If Madame had given me a painting, then that would have been weird."
He put the present in his garage, but when he went to Paris in 2010 to get the works authenticated at the Picasso Administration, the artist's heirs filed an official complaint.
"They don't remember a thing, whether they received this gift in 1970, 1971, 1972," says Jean-Jacques Neuer, Claude Picasso's lawyer.
"If someone gives you 271 Picasso works, you remember that."
The works were all created between 1900 and 1932. "You would have to imagine Picasso keeping them for 70 years and all of a sudden wanting to give them away."
They are not signed either, and Neuer said the artist would always autograph his work — whether he gave it away or sold it.
The couple's lawyer Charles-Etienne Gudin, meanwhile, said there were only a dozen works of value and that the rest was "very mediocre," insisting that Picasso never tried to sell them.