Genevieve Laporte had a two-year secret affair with the artist in the 1950s, when she was in her 20s. The sale was expected to collect no more than $2.4 million.
In the priciest lot, the sketch entitled "Odalisque" was purchased for $575,357 - over three times the estimated price, Artcurial auction house said. The buyer was not identified.
Laporte, now 79, told The Associated Press in an interview this month that she kept the sketches Picasso gave her in a safe because she was worried about thieves, but now was ready to part with them.
"I'm at the end of my road," she said.
The two had their on-and-off affair when Picasso was with the painter Francoise Gilot, the mother of two of his children.
The sketches show Laporte. Most were drawn when Picasso took a break from Gilot in the summer of 1951 to vacation in Saint Tropez with Laporte, the poet Paul Eluard and his wife Dominique.
Many sketches from the vacation bear the inscription "For Genevieve."
One Cubist-style drawing shows Picasso's face hidden in Laporte's tangled hair. When the Hermitage Museum in St. Petersburg showed the sketches, it called them his "Genevieve period," or "Tender period."