In C.E. 71, ZAFT unveils its revolutionary DRAGOON (Disconnected Rapid Armament Group Overlook Operation Network) system in two mobile suits: the YMF-X000A Dreadnought Gundam and ZGMF-X13A Providence Gundam. Unfortunately, the DRAGOONs utilized by these two units can only be controlled by pilots with expanded spatial awareness. However, in C.E. 74, ZAFT introduces the ZGMF-X666S Legend Gundam, an upgrade of the original Providence Gundam design. The Legend Gundam features a new quantum communication system that allows normal pilots to control the DRAGOONs. The Legend Gundam features two types of DRAGOONs, also used by the ZGMF-X3000Q Providence ZAKU. Two beam spike DRAGOONs mounted on top of the backpack are capable of piercing the positron reflector shields used by Earth Alliance mobile armors. Eight general type DRAGOON units are stored on the backpack and waist armor. The Legend Gundam is also equipped with a pair of wrist-mounted "Solidus Fulgor" beam shield generators, which are also used by the ZGMF-X42S Destiny Gundam. The Legend Gundam's armaments are rounded out by a pair of head vulcans, beam javelins and a high-energy beam rifle. The Legend Gundam's systems are powered by a hyper deuterion nuclear reactor. This new design stores power in deuterion form, providing a continuous deuterion charge and, in theory, an endless power supply. However, it is possible for the suit's power to be expended before the reactor can replenish it.

The Legend Gundam is initially assigned to FAITH pilot Athrun Zala by PLANT Supreme Council Chairman Gilbert Durandal. However, after Athrun defects from ZAFT and escapes from the Gibraltar base, it is reassigned to Durandal loyalist Rey Za Burrel. Soon after, the Legend Gundam plays an important role in ZAFT's Operation Ragnarok, an attack on the Alliance's Heavens Base headquarters. Rey, along with Destiny Gundam pilot Shinn Asuka and ZGMF-X56S Impulse Gundam pilot Lunamaria Hawke, destroy five GFAS-X1 Destroy Gundam units guarding the base, paving the way for a ZAFT victory. The Legend Gundam also participates in Operation Fury, an attack on the Orb Union designed to root out Logos leader Lord Djibril. When Djibril escapes to space and fires the Requiem cannon at the PLANTs, the battleship Minerva heads to space and launches an attack on the Alliance's Daedalus lunar base. During the battle, Rey destroys two Destroy Gundams as well as the battleship Girty Lue, killing Djibril. Later, when an Orb space fleet attacks ZAFT to seize control of Requiem, Rey engages Kira Yamato's ZGMF-X20A Freedom Gundam. Rey, a clone of Al Da Flaga, is momentarily confused by Kira's statement that his life is his own. During this moment of confusion, the Legend Gundam is heavily damaged by Kira. Rey then flies to the space fortress Messiah, where he fatally shoots Durandal. Soon after, the damaged fortress crashes into the Moon, presumably destroying the Legend Gundam and killing Rey.