Duo is trained in basic combat, showing skill with firearms throughout the series more so than hand to hand or melee weaponry. He seems to employ a number of technological gadgets when on-foot, such as a special watch and personal beam-propeller glider. As he grew up on the streets, Duo is also quite a fast and agile runner.

As he is a Gundam pilot, Duo has exceptional mobile suit piloting skills, notably being masterful in evasive and other non-combative piloting techniques. In Endless Waltz, Heero all but admits that Duo is the better pilot of the two when they are piloting a shuttle to the X-18999 colony. Duo's specialty in MS combat is stealth and assassination techniques relying on the state-of-the-art cloaking and sensor-scrambling abilities of his XXXG-01D Gundam Deathscythe and XXXG-01D2 Gundam Deathscythe Hell even though he once despised the machine until convinced to use them to become the God of Death; since then he sees Deathscythe as a living being and friend, just like Heero sees Wing Zero as a living being.

Out of the cockpit, Duo seems to be, among all the Wing pilots, the expert at communications and computer-based work such as bugging enemy communications. As a member of the Sweeper Group, he loves to tinker with scrap metal and junk computer bits, even owning a scrapyard with Hilde Schbeiker.

Duo grew up as an orphan in the colony V-08744 of the L2 colony cluster, knowing nothing about his family or real name.[3] In the year After Colony 187, he was a part of a street gang of orphans,[3] which had to steal to survive. Duo adopted his name after the gang leader, Solo, died of a fever.[4] ("If Solo's with me, we'll be Duo.")

Later on, he and the rest of the gang were taken in by the Maxwell Church.[3] The other children were eventually adopted, but Duo's foster parents sent him back[3] and he was adopted by Father Maxwell and Sister Helen, the priest and head nun of the Maxwell Church.[3] During his time at the church, Duo's hair was placed in its recognizable braid by Sister Helen, and he and Father Maxwell exchanged banter about the existence of God with Duo asserting that he didn't believe in God, but in the God of Death, as he'd seen many people die.[3]

The next year, a group of rebels revolted against the occupying the United Earth Sphere Alliance and used the church for shelter. Duo promised to steal a mobile suit for them so that they would leave the church alone[3] and succeeded in securing one but returned to find the church destroyed, Father Maxwell dead, and Sister Helen alive long enough for her to die in Duo's arms.[3] Following the "Maxwell Church Massacre" (which claimed 245 lives) Duo took on the surname Maxwell.[3][4]

In After Colony 192, Duo stowed away on a spaceship owned by Professor G and the Sweeper Group.[3] He was caught but decided to join the Sweeper Group and became a Gundam pilot.[5] Three years later, before Operation Meteor began, Duo refused to go along with Operation Meteor's original plan and attempted to destroy his Gundam but stole it under Professor G's prompting and went to Earth to wage war on OZ.[5]

Gundam Wing
After landing on Earth, Duo destroyed a mobile suit factory in central North America and then attacked an Alliance naval fleet that was attempting to salvage the sunk Wing Gundam. Duo decided to use Wing Gundam as his "back-up" mobile suit unaware the pilot, Heero Yuy, was attempting to destroy it. The two got into a stand-off after Duo came across Heero holding Relena Darlian at gunpoint. Heero was shot during the altercation, but not before blasting his and Duo's Gundams with a set of Torpedoes (though the Gundams were unharmed).

A day later, after recovering Deathscythe and Wing Gundam, Duo broke Heero out of an Alliance hospital and the two used Howard's salvage ship as their base of operations. His suit still damaged during re-entry, Heero used components from Duo's Deathscythe to repair his Gundam overnight and flew off to complete a mission the next morning. Later, Duo encountered Heero again en route to the New Edwards Base where they thought OZ leaders were gathering. This information (leaked by OZ leader Treize Khushrenada) proved to be false as the meeting was actually attended by Alliance pacifists, led by Field Marshal Noventa. The Gundam pilots' attack on the base ended with Heero destroying a shuttle carrying Noventa and the Alliance's other top officials who were seeking peace and Duo would meet the other three Gundam pilots: Trowa Barton, Quatre Raberba Winner, and Chang Wufei.

The God of Death then enrolled in school with Heero as civilian cover until a mission called for them to destroy Taurus mobile suits being transported to a Siberian base. OZ proved more than ready for the Gundams and Lady Une threatened the colonies if they did not surrender and hand over their mobile suits. Heero self-detonated Wing Gundam and Duo escaped with Quatre and the Maganac Corps to their base in the Middle East. The two avoided detection from OZ until the organization began freeing the colonies from the Alliance's control prompting all the Gundam pilots to return to space. His Gundam not equipped for battle in space, Duo was captured by OZ and detained in Colony C-1102. Heero was able to break into his cell with the intent to kill Duo but helped him escape to another colony instead.

Soon after that, Duo watched in horror as Deathscythe was destroyed in a military exercise by Trowa (who was posing as a colony volunteer soldier for OZ). Duo then attempted to destroy the Lunar Base after hearing of the volunteer work there but was captured by volunteer Hilde Schbeiker. He quickly broke loose (not before talking Hilde into re-thinking her decision to join OZ during an interrogation) and made it to the Lunar Base where he was captured again after witnessing his and Wufei's Gundams being rebuilt. He remained imprisoned and almost died from a lack of oxygen when the Romefeller Foundation's chief engineer Tubarov shut off the air to the cells. Lady Une released him, Wufei and the Gundam engineers in time and Duo escaped, taking the incomplete Deathscythe Hell with him.

Now living with Hilde on a colony and staging guerrilla attacks against Romefeller/OZ from the shadows, Duo was tracked down and forced to test Wing Gundam Zero's ZERO System by OZ officer Trant Clark. He ultimately fought Trant with his Deathscythe Hell and watched as the Wing Zero's ZERO System tore the officer's mind apart and killed him. Later, Duo encountered an amnesiac Trowa while visiting the circus with Hilde (Trowa was believed dead after a Quatre went on a rampage with Wing Zero while Duo was imprisoned) and informed Quatre of this soon afterward. After the colony rebel group White Fang approached him to join them and he turned them down, Duo left the colony, not wanting the colony or Hilde to get involved.

Eventually, he saved Trowa, Quatre, and Lucrezia Noin from an OZ attack and the group met up with Duo's Sweeper friend Howard, who was now in space and commanding the spaceship Peacemillion. Heero, Wufei and Sally Po ultimately got to Peacemillion too and Duo worked alongside them to combat the White Fang. During a sortie against the rebel group, Duo had to save Hilde from the rebuilt OZ-13MSX1 Vayeate and OZ-13MSX2 Mercurius mobile dolls (which were programmed with combat data taken from when Heero and Trowa piloted them) after she sneaked aboard the battleship Libra to extract information. Denouncing the prototypes as dolls, Duo swiftly destroyed them both.

In the final battle between the Earth Sphere Unified Nation and White Fang, Duo found the five Gundam Scientists within Libra and flew them to Peacemillion (which had rammed into Libra and was hurtling toward Earth) so they could ignite its engines and send it away from Earth-an act that cost the scientists their lives, but killed White Fang leader Quinze as well. Duo, alongside his Gundam comrades and the Maganac Corps, finally helped destroy a final block of Libra before it entered Earth's atmosphere, bringing an end to the Eve Wars.

Endless Waltz
After working with Quatre to send four of the Gundams into the Sun, Duo accompanied Heero in his attempt to rescue Relena after she was captured by Mariemaia Khushrenada (the illegitimate daughter of Treize). During their entrance to the colony, he captured a Leo and fought Trowa (who had infiltrated the Mariemaia Army) in a Serpent briefly before escaping. Duo eventually helped Heero and Trowa prevent Colony X-18999 from being dropped onto Earth and was captured to allow Heero to escape. He was able to quickly break out of a brig, met Sally Po and Trowa on a shuttle, and rendezvoused with Quatre (who had returned with the Gundams) in space. He then descended to Earth with Trowa and Quatre and fought alongside Zechs and Noin in Brussels, disabling numerous Serpent suits of the Mariemaia Army without killing any pilots. After Dekim Barton shot Mariemaia and was shot and killed by a Treize loyalist, the conflict ended and Duo, along with Quatre and Trowa, self-detonated Deathscythe Hell and their suits. Duo was last seen eating lunch with Hilde on one of the colonies.