Simone Mastrelli entered a guilty plea at Preston Crown Court to unlawfully and maliciously inflicting grievous bodily harm on Cox, who spent four-and-a-half weeks in a specialist neurological unit at Liverpool's Walton Centre following the attack.
The 53-year-old was then transferred to Beaumont Hospital in Dublin and continues his recovery from serious catastrophic head injuries at Ireland's National Rehabilitation Hospital in Dun Laoghaire.
Mastrelli pleaded not guilty to a separate count of violent disorder, which will lie on file after the court accepted his plea.
Detective Inspector of Merseyside Police Paul Speight said: “The shocking and completely unprovoked assault of Sean Cox was rightly met with disgust and abhorrence by people in Merseyside and across the world.
"As a passionate Liverpool fan, Sean had travelled to the city to enjoy the occasion of a Champions League match. But before he had even had opportunity to enter the stadium, Sean was brutally attacked by Simone Mastrelli.
"Instead of watching his favourite team, Sean ended the evening in a critical condition in hospital and has spent the past 10 months receiving round-the-clock care. His long road to a full recovery continues and he will carry the physical and emotional scars of that night for the rest of his life.
"Football fans should be able to attend matches without fear of being subjected to such a vicious attack, and I hope today's sentencing sends a clear message that anyone who seeks to bring violence to a sporting event will face the full force of the law.
"The fact that Mastrelli left the country after the assault in a failed bid to evade justice has only prolonged the anguish for his Sean and his family. I hope the fact he was arrested shows we and colleagues around the world will not be deterred from the pursuit of justice.
"The impact this incident has had on Sean and his family cannot be underestimated and I hope that the jailing of Mastrelli today, together with the outpouring of support the family have received, provides them with some comfort as they continue to adjust to lives that have been forever changed by the events of that night."
Last October, 21-year-old Roma fan Filippo Lombardi was cleared of inflicting grevious bodily harm on Cox but found guilty of violent disorder and sentenced to three years in jail.
Daniele Sciusco, 29 from Rome, admitted violent disorder and was jailed for two-and-a-half-years three months earlier.
DI Speight added: "I want to take this opportunity to thank the team of detectives who investigated the attack, as well as the authorities in Italy who assisted the apprehension and extradition of Mastrelli so he could face justice today."