The couple for years squirreled away the staggering trove - which is believed to be authentic, but whose origin is unclear - in their garage on the French Riviera, said Picasso Administration lawyer Jean-Jacques Neuer.
The cache, dating from the artist's most creative period from 1900 to 1932, includes lithographs, portraits, watercolors, and sketches - plus nine Cubist collages said to be worth euro40 million alone, according to French daily Liberation, which first reported Monday on the discovery.
Pierre Le Guennec, a 71-year-old former electrician who once worked for Picasso, and his wife showed many of the works to Picasso's son Claude and other estate administrators in Paris in September seeking to have the works certified as authentic, the lawyer said.
Shortly after that meeting, Neuer filed suit on behalf of Picasso's heirs for alleged illegal receipt of the works - and police investigators are looking into how Le Guennec and his wife came by the pictures.
The couple said that they were given the works by Picasso and his wife, Jacqueline, according to a police official, who spoke on condition of anonymity because the investigation is under way.
Claude Picasso, quoted in Liberation, noted that his father was known for his generosity - but that he always dedicated, dated and signed his gifts, as he knew that some recipients might try to sell the works one day.
"To give away such a large quantity, that's unheard-of. It doesn't hold water," Claude Picasso was quoted in Liberation as saying. "This was part of his life."
To some, the emergence of the works by the 20th century's most renowned artist is akin to opening a time capsule, or a discovery on par with the recent publication of Mark Twain's 100-year-dormant autobiography.
"Claude Picasso was astounded. He couldn't believe his eyes," said Neuer. "Just about everybody has felt that way ... when you have 271 Picasso works that were never seen, never inventoried - that's just unprecedented."
New York's Metropolitan Museum of Art says Picasso produced more than 20,000 works of art during his long career. Hundreds have been listed as missing - a number so large in part because he was so prolific.
The AP attempted to reach Le Guennec by phone, but no one answered. Liberation said the former electrician claimed to have worked at three of Picasso's residences - and once installed a security alarm system for the artist.