Vania Vannucchi, a health worker, suffered second and third degree burns across 90 percent of her body after being doused in a flammable liquid and set alight.
She died of her injuries at Pisa's Cisanello hospital on Wednesday morning.
Pasquale Russo, who works for a cooperative within the healthcare sector, has been arrested for attempted murder, La Repubblica reported.
Before being sedated, Vannucchi managed to repeatedly tell paramedics that Russo, a married father-of-three, was her alleged assailant.
She was attacked behind a shed in an area of Lucca where a former hospital, now a centre for medical tests, was based.
Her screams were heard by some of the centre’s staff, who rushed to her aid and found her lying on the ground with her dress on fire. They immediately raised the alarm and tried to put the fire out with buckets of water.
Russo, who was found at home by police washing his work clothes and with two wounds on his arm, denies the charges.
In June, a 27-year-old security worker admitted burning his ex-girlfriend, 21-year-old Sara Pietrantonio, to death.
Vincenzo Paduano told investigators that he couldn't accept that she'd abandoned him.
Di Pietrantonio became the 55th "femicide" victim in Italy between January and June - three more were murdered by either a spouse, boyfriend or ex within the weeks that followed.
Last year, 128 women were victims of femicide, the year before there were 136. Thousands more have suffered domestic abuse or are stalked by men.