As a wild Pokémon
Clemont and Luxray first met in Clemont's youth, when he was studying at an academy specializing in Electric-type Pokémon and Luxray was still a Shinx. Clemont was taking a recreational stroll, thinking of an idea for his graduation assignment. He then found Shinx, visibly weakened by electricity loss. Without hesitation, he brought him to a nearby Pokémon Center, where he was quickly healed. At night, when Clemont was working on his research, Shinx knocked on his window, and Clemont opened it to let him in. He showed Shinx the idea he was working on and that would prevent Electric-type Pokémon from suffering electricity loss. Clemont and Shinx then gradually became good friends, playing together, sleeping together, and working together on Clemont's graduate research.
Clemont's graduate research was a success, and it was enough for him to complete his studies. The day before his graduation, Clemont had promised Shinx to meet up so he could thank him for giving Clemont the idea for his graduate research and wanting to ask him to become his partner. He had even brought a cake for him, but on his way the mayor of the academy's town came to him, compelling him to come with him as a ceremonial meal had been organized to celebrate Clemont's graduation. Looking from the window of the mayor's car, Clemont watched in agony as he saw Shinx waiting for him. After the meal, Clemont came back to their meeting spot, but Shinx was nowhere to be seen, having left in disappointment thinking Clemont had abandoned him. Clemont returned to his home in Lumiose City, while Shinx remained a wild Pokémon, still roaming around the academy. Sometime later, Shinx eventually evolved into Luxio.
In the present day, Luxio was first seen spying on Ash and his friends from a rooftop as they visited the academy. He later showed up when Team Rocket was causing trouble at the electricity system Clemont had built. Ash and his friends also showed up, and Clemont recognized Luxio, even though he had evolved. Although he briefly seemed to recognize Clemont in return, Luxio ran away, still angry about Clemont not showing up at their meeting. He later battled Team Rocket when they managed to steal a large amount of electricity from the town. When Clemont jumped in the way to shield Luxio from one of Team Rocket's attack and took the hit, Luxio remembered the good times they had together. After Team Rocket was defeated, Luxio proceeded to walk away. Before he left, Clemont admitted he had broken his promise before, but that it was now his turn to wait for Luxio. He proposed to meet up at the same meeting spot as before, and that Luxio should come if he wanted to join Clemont's team. The next day, although it seemed as if Luxio had not forgiven Clemont after all, he showed up just when Clemont had given up hope. Overjoyed, Clemont threw a Poké Ball at him and caught him.
In The Future Is Now, Thanks to Determination!, Luxio was present with Clemont in the Lumiose Badlands, until he was hypnotized by a machine in the Kalos Power Plant along with Pikachu and Dedenne, they attacked their Trainers and were ordered inside the plant, along with the other Electric-type Pokémon who were also hypnotized, it was later revealed that it was the work of Team Rocket. On their command, he attacked Ash who was trying to break Pikachu free from their influence. Afterwards, Clemont decided to try and break Luxio free as well, but Luxio attacked him with Thunder Fang and then Clemont hugged him while he used Discharge. Clemont partially regained control by using his Aipom Arm, by attaching it to the electric current and having Luxio increase his power on its discharge. The discharge broke the satellite dishes controlling the Pokémon, setting the Pokémon free. He caught Clemont as he fell from exhaustion and began to evolve into Luxray, while Team Rocket tried to reboot their satellite dishes. After evolving he used his new move, Electric Terrain, to destroy the satellite dishes and increase the power of Electric-type moves. This allowed the Electric-type Pokémon to send Team Rocket blasting off. He later went with Clemont to Lumiose City by helicopter to train for Clemont's upcoming Gym battle with Ash.
In Battling with Elegance and a Big Smile!, Luxray was used in a Gym battle against a Trainer named Sawyer. It easily defeated his Treecko with Wild Charge despite being at a type disadvantage. This helped to boost Clemont's confidence for his Gym battle against Ash.
In Confronting the Darkness!, Clemont used Luxray to battle Belmondo's Magnezone. Magnezone used Zap Cannon, which Luxray dodged and hit with Wild Charge. Magnezone then used Electro Ball, which Luxray was able to reflect back with Swift. Luxray then defeated Magnezone with another Swift.
In The Moment of Lumiose Truth!, Luxray was used in a Gym battle and his final choice against Ash. He first went up against Hawlucha. Hawlucha hit Luxray with Flying Press, but he responded with Electric Terrain, increasing the power of his Electric-type moves. Hawlucha used High Jump Kick, whilst the Gleam Eyes Pokémon used Wild Charge, overpowering Hawlucha and knocking it out. Luxray next went up against Pikachu, who could also use Electric Terrain to an advantage as well. Pikachu started with Thunderbolt and was blocked by Luxray's Thunder Fang. He then used Wild Charge and scored a direct hit. Luxray followed up with Swift but Pikachu was able to deflect it with Iron Tail. Luxray countered with another Wild Charge and was able to knock Pikachu out. Luxray finally went up against Ash's final Pokémon, Goodra. Ash remembered pouring water on Goodra, when he met it as a Goomy, so he had Goodra use Rain Dance, nullifying the Electric Terrain and curing itself of the paralysis previously caused by Heliolisk's Thunder Wave due to its Hydration ability. Luxray used Swift, which Goodra countered by punching the Swift stars and deflecting them with its tail back to Luxray, but Luxray was able to dodge this and use Thunder Fang. However Goodra blocked this attack with its tail and sent Luxray back. Luxray then hit with Wild Charge and used Swift on Goodra, but Goodra countered with Bide, using the power from Luxray's powerful attack to deal major damage to him. This created a powerful explosion, but at the end, only Goodra was able to remain standing and Luxray was knocked out. This won Ash the battle, earning him the Voltage Badge.
In From A to Z!, Luxray was sent out to battle Celosia and several Team Flare Grunts, alongside Ash's Pikachu and Frogadier, Serena's Braixen and Sawyer's Grovyle, to protect Squishy. He was then recalled when Clemont, Serena and Bonnie fled with Squishy. In Meeting at Terminus Cave!, Luxray used his X-ray sight to navigate through Terminus Cave alongside Clemont's searchlight, Braixen's fire, and Noibat's ultrasound. He was later used to face Team Flare again, but the battle stopped when Squishy defeated Team Flare's Pokémon.
In The Synchronicity Test!, Luxray was sent out to spar with Ash's Greninja to try and trigger Greninja's transformation into Ash-Greninja. Luxray started the battle by powering up his Electric-type moves using Electric Terrain and then countered Greninja's Cut with Thunder Fang, pushing the Ninja Pokémon back. Luxray then used Wild Charge to cancel out Greninja's Double Team. Double Team, however, was a distraction, and Luxray was struck hard by a surprise Aerial Ace. After clashing with Thunder Fang and Cut again the battle was stopped, since both Pokémon were tired and Greninja's transformation still hadn't taken place.
Luxray later helped to combat the giant roots that were growing over Lumiose City in A Towering Takeover!, after Team Flare launched their attack. He battled Bryony's Liepard and Aliana's Druddigon in the following episode. Luxray, alongside Bunnelby, Chespin and Heliolisk defeated the Team Flare Scientists' Pokémon, allowing Clembot to subdue them and for the team to infiltrate the Lumiose Gym. In The Right Hero for the Right Job!, Luxray used Electric Terrain to incapacitate several Team Flare member grunts on the Gym's battlefield. He then battled Xerosic's Crobat and Malamar, which resulted in his victory and allowed Clembot to evict Xerosic from the Gym. Luxray was used again in Forming a More Perfect Union!, where he joined the fight against the Giant Rock.
In Battling With a Clean Slate!, Luxray and the rest of Clemont's Pokémon received medals from Professor Sycamore for their heroic efforts against Team Flare.
As a Shinx, he was shown to be playful and friendly, especially with Clemont due to being rescued by him. After evolving into a Luxio, he became stoic, serious, and focused, although this could be due to Luxio being angry at what he thought was Clemont abandoning him. After Clemont rescued him again, Luxio become loyal to him and allowed himself to be caught, this was shown again in The Future Is Now, Thanks to Determination! where he was able to break free from Team Rocket's control, which allowed him to evolve into Luxray. He maintained this loyalty and affection after evolving. He also seems to be somewhat stubborn as he kept fighting Team Rocket even though they managed to hit him several times.
Luxray is a very strong battler, as Clemont uses him as his most common battling Pokémon, being used in battles against Ash at the Lumiose Gym, Team Rocket, the Ninja Army, and Team Flare.
Luxray also appears to be extremely friendly towards Ash, as shown in So You're Having A Bad Day!, where he ran and jumped up on Ash when they were reunited.