The two systems will be transmitted on the same radio frequency so that users will be able to use them in combination, allowing for greater accuracy of images and information.
"The agreement to jointly use ... these interoperable civil signals demonstrates the close US and EU cooperation since 2004 to ensure that the Global Positioning System and Galileo are compatible and interoperable at the user level," said a European Commission statement.
The European Commission is hopeful that the agreement will help to ensure that Galileo, which has yet to be launched, will be accepted alongside its popular rival, GPS.
The agreement's success may also depend on whether the makers of receivers design devices that integrate the two systems.
Galileo still years away
The US has 30 satellites transmitting information which users of car navigation system and other devices can employ to chart their own location or that of others. The EU plans to have just as many satellites in orbit by 2010 and to launch Galileo in 2012.
The EU has mooted Galileo as a key technology project. Last month, EU ministers said taxpayers would have to make up for a 2.4 billion euro ($3.29 billion) shortfall, after the private sector shied away from footing the bill.
China is also developing a satellite navigation system.