The country's Ministry of Defense said the status was marked with a ceremony at Tengah Air Base.
"The G550-AEW, together with the (air force's) fighter squadrons and ground-based Air Defense units, are a powerful network that represents a quantum jump in the (air force's) ability to identify potential aerial threats early and respond decisively, in peace or in war," said Minister for Defense Ng Eng Hen.
G550-AEW aircraft are replacing the service's E-2C Hawkeyes. It has a flight duration of nine hours compared to the E-2's six hours and can climb to 41,000 feet. It has a detection range of more than 200 nautical miles.
The squadron has four of the Gulfstreams. The first was delivered in early 2009 and the last was delivered in October.