Mariam Yahya Ibrahim, whose sentence and detention triggered international outrage, walked off the aircraft cradling her baby and was greeted by Italian prime minister Matteo Renzi.
There were no details on what led up to the 27-year-old's departure after a month in limbo in Khartoum, but a senior Sudanese official said it had been cleared by the government.
"The authorities did not prevent her departure that was known and approved in advance," the senior official told Reuters, speaking on condition of anonymity.
Ibrahim was accompanied on the plane by Italy's vice minister for foreign affairs, Lapo Pistelli. He told journalists at Rome's Ciampino airport Italy had been in "constant dialogue" with Sudan but did not give any more details on Rome's role in securing her exit.
He published a photograph on his Facebook page of himself with Ibrahim and her two children on the plane with the caption: "A couple of minutes away from Rome. Mission accomplished."
Ibrahim was sentenced to death in May on charges of converting from Islam to Christianity and marrying a Christian South Sudanese-American.
POPE "HAPPY AND GRATEFUL"
The conviction was quashed last month, but Sudan's government accused her of trying to leave the country with falsified papers, preventing her departure for the United States with her husband and two children.
She was initially detained, then released and moved into the U.S. embassy in Khartoum.
Pistelli told reporters at the airport that the family was in good health and would stay in Italy for a few days before departing for the United States.
Pistelli, who carried one of Ibrahim's young children off the plane, said he expected her to have "some important meetings" during her time in Italy. Asked whether she might meet Pope Francis, Pistelli said:
"I don't know the pope's agenda. The pope was informed about this by the prime minister and said he was happy and grateful," Pistelli said.
Vatican spokesman Father Federico Lombardi said that no such meeting was currently in the pope's diary.
Ibrahim says she was born and raised as a Christian by an Ethiopian family in Sudan and later abducted by a Sudanese Muslim family.
The Muslim family denies that and filed a lawsuit to have her marriage annulled last week in a new attempt to stop her leaving the country. That case was later dropped.
Prime Minister Renzi mentioned Ibrahim's case in his speech to inaugurate Italy's six-month European Union presidency earlier this month.
"If there is no European reaction we cannot feel worthy to call ourselves 'Europe'," Renzi said.
Muslim women are not permitted to marry Christian men under the brand of Islamic law enforced in Sudan.