The "technical understanding", which updates a serious crime accord from 2009, was signed by Italian Interior Minister Marco Minniti and Elaine Duke, acting US Homeland Security Secretary.
The pair were at a G7 interior ministers meeting in Italy dedicated to working out how to deal with a potential flood of foreign fighters returning to Europe after the fall of IS stronghold Raqa in Syria.
Rome and Washington will be able "to access data contained in the national identification fingerprint systems" in a move "to create a network to verify the identity of migrants, asylum seekers or refugees".
The aim was "to ascertain whether they are noted criminal suspects or terrorists", Italy's interior ministry said in a statement.
Thousands of citizens of Western countries travelled to Syria and Iraq to fight for IS between 2014 and 2016, including some who then returned and staged attacks that claimed dozens of lives.
Minniti has warned fighters fleeing after the fall of Raqa could take advantage of the confusion and "use the human trafficking routes" to return home – raising the spectre of extremists embarking on the migrant boats which regularly head from Libya to Italy.