Luca Attanasio, 43, died in hospital on Monday after the United Nations convoy he was travelling in came under fire near Goma, a statement said.
The convoy reportedly belonged to the UN’s World Food Programme (WFP).
An Italian military police officer travelling with the envoy and a third person were also killed, reports say.
“It is with deep sadness that the foreign ministry confirms the death, today in Goma, of the Italian ambassador,” the ministry’s statement said.
Foreign Minister Luigi Di Maio expressed his “great dismay and immense sorrow” at the killings.
“No effort will be spared to shed light on what happened,” he said.
The attack is believed to have been an attempted kidnapping, according to officials at the nearby Virunga National Park.
It happened at around 10:15 local time (08:15 GMT) just north of Goma, the officials told Reuters news agency.
It is not clear who was behind the attack, but many armed groups are known to operate in and around the park.
Militias also clash regularly in the east of the country, where a large UN force is struggling to keep the peace.
Mr Attanasio had represented Italy in the DR Congo since 2017. He joined the diplomatic service in 2003 and spent time in Morocco and Nigeria.
DR Congo was for many years at the centre of a brutal civil war that drew in several neighbouring countries.
The conflict led to the loss of some five million lives between and 1994 and 2003, with some observers branding it Africa’s Great War.
But the end of the conflict did not mark an end to the violence. Dozens of militias and rebel groups continue to operate in eastern areas.
The UN’s peacekeeping mission has been in DR Congo since 1999. It is one of the biggest peacekeeping operations in the world, with more than 17,000 personnel on the ground.