The series is set in 2307 AD.^[6] As a result of the depletion of fossil fuels, humanity had to search for a new source of power. The power was found in the form of massive arrays of solar power collectors orbiting the Earth, and supported by three orbital elevators, each one serving one of the three "power blocs" on the planet, namely Union, controlling the region surrounding North America; Human Reform League (Sino-Japanese: 人類革新連盟; Romaji: jinrui kakushin renmei; Pinyin: rénlèi géxīn liánméng), consisting of China, Russia and India; and AEU, which controls mainland Europe.^[7] With this nearly inexhaustible source of energy benefiting only the major powers and their allies, constant warfare erupts around the globe among minor countries for fuels and energy. Countries that once economically relied on the sale of fossil fuels have plunged into poverty. Some even believe that solar energy threatened the "promised land of God", resulting in the 20-year Solar Wars. This chaos led to the formation of a private military organization, called Celestial Being (ソレスタルビーイング Soresutaru Bīingu^?), dedicated to eradicating war and uniting humanity through the use of four advanced machines called Gundams.^[1][3] Mobile Suit Gundam 00 follows four mobile suit pilots termed Gundam Meisters ( ガンダムマイスター Gandamu Maisutā^?), sided with Celestial Being. The main protagonistis 16-year-old Setsuna F. Seiei, a taciturn Gundam pilot who grew up in the war-torn Republic of Krugis.^[8][9]

Unable to counter Celestial Being's superior technology, the three major powers eventually unite into the United Nations Army in order to counter Celestial Being's armed interventions.^[10] In order to fight the Gundams, the United Nations Army employed the help of Laguna Harvey. Harvey, a Celestial Being intelligence agent turned traitor, provides them with 30 GN-X, mobile suits equipped with pseudo-GN Drives. As the United Nations resist Celestial Being's interventions, a second team of Gundams, known as Team Trinity, appears and assists in the Meisters' eradication of war, albeit in a much more cruel and cold-blooded fashion.

Alejandro Corner, a former Celestial Being observer who plans to make use of the chaos and destruction created by Celestial Being to rule a reconstructed world, subsequently takes over Veda, Celestial Being's supercomputer which is believed to be located in the moon somewhere (you find out its location in the 2nd season). Without the tactical aid from the organization's artificial intelligence, Celestial Being is easily overwhelmed and overpowered by GN-X units and their superior numbers.

The United Nations Army initiates Operation Fallen Angels to destroy the Gundams, having discovered the location of the Meisters' mothership, Ptolemaios. During the operation, Ali Al-Saachez kills Lockon Stratos after a climactic battle (Lockon Statos was just injured in a previous battle). Alejandro Corner, in his unique custommobile armor Alvatore, attacks Setsuna as the GN-X units proceed to destroy the Ptolemaios and the remaining Gundams. Setsuna struggles with the monstrous Alvatore, but in the end succeeds in killing Alejandro. Graham Aker, an ace pilot of the United Nations Army, then challenges Setsuna to a fight, seeking revenge for his fallen comrades and questioning the purpose of Gundams' existence. The fight results in the destruction of the GN-Flag, while the Exia is heavily damaged.