The 31-year-old killer smiled, laughed and looked disinterested throughout most of her sentencing hearing at London's Old Bailey.
Mr Justice Spencer - who described her as "a cruel, calculating, selfish and manipulative serial killer" - said her three murders were so serious that they warranted a whole life tariff.
The judge revealed that Dennehy sent him a letter saying she was not sorry for the murders.
He added that she told a psychiatrist: "I killed to see how I would feel, to see if I was as cold as I thought I was, then it got more-ish."
As she was led from the dock, she remained passive and composed.
Dennehy, of Orton Goldhay, Peterborough, pled guilty at an earlier hearing to the murders of Lukasz Slaboszewski, 31, Kevin Lee, 48, and John Chapman, 56, in and around Peterborough over a 10-day period last March.
Police launched a nationwide hunt to find her after the bodies were discovered in remote ditches in Cambridgeshire, but she drove 140 miles to Hereford, where she repeatedly stabbed two dog walkers.
Dennehy, who wore a pink Adidas vest top in the dock while flanked by 10 security guards and her three accomplices, has also admitted two counts of attempted murder and preventing the lawful and decent burial of her murder victims.
Mr Lee's wife Christina said in a statement afterwards: "We feel Joanne Dennehy brainwashed Kevin, causing him to make a bad decision, and he has paid for that with his life."
Mr Justice Spencer said to Dennehy, who has been diagnosed with various psychopathic disorders : "Although you pleaded guilty, you've made it quite clear you have no remorse."