A federal court jury also found Gilberto Valle, 28, guilty on a lesser charge of improperly accessing a law enforcement database to gather personal information about potential targets, including his now-estranged wife.
Prosecutors said Valle, 28, who was dubbed the "cannibal cop" by the tabloid media, crossed the line from fantasy to reality by taking specific action in conspiring to kidnap women.
Valle's attorney, Julia Gatto, argued that her client was merely engaged in online fantasy role playing.
When he is sentenced on June 19, Valle faces up to life in prison on the charge of conspiracy to kidnap and up to one year in prison for the database breach.
His lawyers said they would appeal.
"This is a dangerous prosecution when we start opening up our minds and prosecuting what's inside our brains and not in the real world," Gatto said. "We totally believe the government did not prove their case and the jury couldn't get past the thoughts."
US Attorney Preet Bharara said the jury found Valle had taken a step into the real world and the criminal realm.
"Today, a unanimous jury found that Gilberto Valle's detailed and specific plans to abduct women for the purpose of committing grotesque crimes were very real, and that he was guilty as charged," Bharara said in a statement. "The Internet is a forum for the free exchange of ideas, but it does not confer immunity for plotting crimes and taking steps to carry out those crimes."
Valle and Gatto hung their heads as they sat side by side awaiting the verdict. When the jury read "guilty" their shoulders slumped in unison. Moments later, as they stood, Valle shook his head then draped his arms around Gatto, tears welling in his eyes.
Judge Paul Gardephe commended the jury of six women and six men, who had deliberated since Thursday, for reaching a verdict in the often grisly trial. Evidence included "human meat recipes" and images of women being roasted on a spit.
"Sitting in judgment of another human being is difficult. This case in particular has not been an easy one ... (with) material that degrades the human spirit," Gardephe told the jury.
Federal prosecutor Hadassa Waxman said in her closing argument that Valle was at one point engaged in fantasy, but his intentions had grown more sinister.
Pointing to his extensive online research on kidnapping, making chloroform and cooking women, she said, "These are real searches conducted to carry out real research to kidnap real women."
Gatto, the defense lawyer, told jurors that after nearly a year of fantasizing about approximately two dozen women - in many cases discussing kidnapping with other fetishists - none of the plotters had ever met, exchanged money or committed any crimes.
Valle did not take the witness stand. His now-estranged wife Kathleen Mangan, 27, was the first prosecution witness in the case and testified about how last fall she discovered her husband's plans to torture her when she looked on her laptop, which he had been using.
She said she read how she was to be tied up and her throat slit.
The former New York City schoolteacher testified that she contacted authorities and fled with their young daughter to live with her parents in Nevada.
The trial brought to light a macabre cyberspace community where millions of people discuss and exchange images and video of extraordinary brutality, much of it staged.
Defense attorneys took jurors on a video tour of DarkFetishNet.com, a website at the heart of Valle's case.
In a videotaped deposition, its creator, Russian Internet entrepreneur Sergay Merenkov, likened it to Facebook. Instead of family photos and videos of pets, however, members share photos and videos demonstrating extreme cruelty including rape and asphyxiation, with the goal of sexual stimulation.
Merenkov said that he had kicked members off the website when "it seemed not to be fantasy anymore."