Emmanuel Chidi, 36, was walking with his girlfriend in the heart of the small town of Paolo Calcinora on Tuesday, when they had racial abuse heaped on them by the supporter of a local football club, the Agi news agency reported.
That led to an altercation and Chidi was brutally beaten on the head until he fell to the ground. He never recovered consciousness and died in hospital on Wednesday.
"As mayor of a town that is welcoming and open to integration, I feel I'm living in a nightmare," the town's mayor said.
Chidi had been living in the area for eight months and was lodged in a shelter run by Catholic charity Caritas.
His girlfriend had lost her baby after a perilous Mediterranean crossing.
Hundreds of migrants arrive daily in Italy. The Italian interior ministry said last week that a total of 70,930 people landed between January and June -- almost exactly the same number as the same period in 2015 and only slightly higher than in 2014.
The full-year total of migrant arrivals for 2015 was 153,000.