Osman Matammud, who is originally from Somalia, was convicted of multiple counts of abduction for ransom and sexual violence against young women and girls.
The Court of Assizes in Milan came to the decision after five hours of deliberation.
The court heard testimonies of 17 witnesses who told of how they had been beaten or raped by Matammud at the Bani Walid detention centre in Libya.
Prosecutors said he behaved like a Nazi concentration camp guard at the squalid and overcrowded facility located in the Libyan desert.
"I'm not Somali, I'm not Muslim – I'm your boss," Matammud allegedly told the migrants he was abusing, many of whom came from his home country of Somalia.
Investigators were told by a number of Somali women that Matammud raped them several times as part of his abuse that aimed to pressure migrants' families into paying extortionate fees for their detained relatives' passage to Europe.
"The first night, he came into the hangar, he grabbed me and he ripped off my clothes in front of everyone. He penetrated me. I fainted but when I came to, there was blood everywhere. I was raped many times by him – every night," one teenage girl told prosecutors.
Motammud was captured by Italian police last year as he attempted to pass himself off as an asylum seeker at a refugee centre in Milan.
He was recognised by Somali migrants also at the centre, who attempted to lynch Motammud when they realised it was him.
The altercation was stopped by Italian police who intervened and arrested Motammud.
Motammud is set to begin his life sentence with three years in solitary confinement.
He denies all charges and his lawyers say he will be appealing the verdict.
The trial has once again highlighted the squalid conditions endured by migrants who undertake the perilous journey through Libya and across the Mediterranean into Europe.
In the last year, human rights groups have reported a number of cases of abuse, murder and enslavement of migrants in Libya.
"In a career spanning 40 years, I've never come across such horrors. And what is going on in Bani Walid is going on in all the transit camps," Ilda Boccassini, chief prosecutor prosecutor in the case, said following Motammud's sentencing.