He was dispatched by his master to locate Queen Padmé Amidala, who had slipped through the grasp of the incompetent leaders of the Trade Federation. He forged a distress call from Sio Bibble to trick someone on the Queen's starship to respond so he could trace the signal to its position on Tatooine. Once on the planet he dispatched probes to search for the Queen's or ship's exact location. He raced to the scene just as the ship was taking off again.
Sidious then ordered his apprentice to Naboo to wait for the Queen there. When Amidala lead an attack on the Theed palace, Maul intercepted the small band and engaged their two Jedi knights in battle. He was able to hold his own against Qui-Gon Jinn and Obi-Wan Kenobi together. However, once he isolated Qui-Gon, he was able to kill the Jedi Master.
Obi-Wan, enraged at the death of his friend, initially caught Maul off guard and cut the Sith's lightsaber in two. Maul quickly recovered and used the Force to push Obi-Wan over the edge of a deep shaft. However, Maul made the same mistake that most villains make and took a moment to gloat over his enemy, kicking Kenobi's sabre down the shaft and sending showers of sparks down onto the padawan's head. Obi-Wan seized the moment to fling himself out of the shaft, retrieve his master's sabre, and slice Maul in half. The last we saw of the Sith apprentice was the two halves of his body falling down the apparently bottomless pit.
In Star Wars: The Clone Wars, Maul somehow survived the fall and managed to get his lower torso replaced with bionics, allowing him to return to threaten Obi-Wan Kenobi for years to come.