Mohammed Ali, 31, was convicted at the Old Bailey of attempting to possess a chemical weapon after around five and a half hours of deliberations by a jury.
Ali, from Liverpool, struck a deal with a supplier to buy 500mg of powder - enough to kill 1,400 people.
He was unaware that his source was in fact an FBI agent.
The trial heard the father-of-two was sent harmless powder hidden inside a toy car.
After opening the package, which had been treated with a marker substance, he was arrested at his home the following morning.
Under ultraviolet light, Ali's face lit up, showing he had handled the parcel.
Ali told jurors he was just "curious" and wanted to test the boundaries of the Dark Web, and was unaware that ricin was illegal.
He told the court: "I was interested in the Dark Net and ricin. I just wanted to know what the fuss was about.
"I found lots of different items ranging from drugs, guns, other illegal items, and because I had been watching Breaking Bad I just had ricin in my mind."
His defence team suggested Ali wanted ricin for a "peaceful purpose" and a psychologist told jurors he exhibited signs of Asperger's syndrome.
But prosecutor Sally Howes QC said he was a "chancer" who lied to police about having ricin when he was arrested in the hope that he would "get away with it".
Judge, Mr Justice Saunders said: "There is no evidence that he was planning any sort of terrorist attack.
"There is also no evidence that he had in mind any specific victims for ricin. I do not accept he was going to dispose of it.
"I'm satisfied it would have remained in his possession in some way and that is the basis on which I propose to sentence."
Ali had previously been involved in various illegal money-making scams which included stealing Â£250,000 from PayPal through a loophole, the court was told.
Sue Hemming, from the Crown Prosecution Service, said: "Ricin is a naturally occurring poison which is fatal even in very small doses. Ali knew the dangers of ricin and had been researching poisons for months before he attempted to obtain it.
"Today shows yet again that even in the case of crimes committed in the darkest corners of the internet, criminals can be caught and convicted."
A man has been found guilty of trying to buy deadly ricin poison from the Dark Web after being inspired by the hit US television series Breaking Bad.