Felonious Gru is a super-villain, operating out of his suburban home that serves as a front for an underground lair where he, his partner, Dr. Nefario, and thousands of short yellow minions (to whom he shows considerable affection) plan their nefarious deeds. When Gru learns that another super-villain has stolen the Great Pyramid of Giza, his pride is injured, and he plans an even greater heist, stealing the Earth's moon, a plan he has had since childhood but discouraged by his mother. The prospect is quite expensive, and Gru seeks out a loan from the Bank of Evil (formerly "Lehman Brothers", as it says on the bank door). The Bank's president, Mr. Perkins, initially refuses to extend Gru a loan, noting that he is much older than the super-villains of the day, but offers that if he can secure a shrink ray, the critical part of Gru's plan, the Bank will give Gru his loan.
Gru is able to steal a shrink ray from a classified East Asia facility, but it is stolen from him moments later by Vector, a nerdy super-villain who is responsible for the Pyramid theft. Gru attempts to break into Vector's lair but is easily defeated by the numerous defenses. Taking a moment to re-plan, he watches as three orphan girls, Margo, Edith, and Agnes, enter Vector's lab with no difficulty to sell him cookies. Gru devises a scheme to use the girls to take in robotic cookies that can be used to disable the lair's defenses and allow him to steal the shrink ray. He adopts the three girls from the local orphanage, Miss Hattie's Home for Girls, falsifying his credentials, but has difficulty coming to nurture them properly between their own rambunctiousness, their ballet classes, and his own unwillingness to be a parent.
Gru is eventually able to set his plan in motion, and with the girls' help, retrieves the shrink ray. The girls suggest going to a theme park to celebrate, which Gru agrees to, seeing it as a way to abandon the girls. However, when he is forced to accompany the girls on one of the rides he finds himself coming around and enjoying his time. Gru and the girls spend the entire day at the park, Gru having warmed up to them.
With the shrink ray in hand, he contacts Perkins at the Bank and successfully shows his plan to steal the moon to him. Though Perkins is impressed by Gru's plan, he still refuses to give Gru a loan, stating that Gru's schemes always seem to fail and that the Bank is going to support a younger villain. Perkins then calls Vector, who is revealed to be Perkins's son, to his office and informs him that Gru has stolen the shrink ray from him. Encouraged by the girls who want to see Gru succeed by giving him the few coins in their piggy bank, Gru decides to scavenge parts from his lair to construct the rocket that will take him to the moon. Gru plans to launch on the day the moon is in the best position in Earth's orbit, but which happens to be the same day of the girls' ballet recital. Dr. Nefario feels that Gru is not focused in his mission and the girls are becoming the major distraction, so he calls Miss Hattie telling her that Gru wants to return the girls, which he sadly does when Miss Hattie arrives.
Gru launches his rocket and successfully shrinks the moon, and sees he has time to make it to the girls' recital. By the time he lands the recital is over, but Vector has left a ransom note, having kidnapped the girls and demanding the moon in exchange for the girls. Matters are made worse when Dr. Nefario realizes that "the larger the mass of the object, the quicker the effects of the shrink ray wear off". Gru instantly commits to the exchange but Vector reneges on the deal, taking both the moon and the girls in his own ship. As the shrink ray's effect wears off and the moon expands, Gru, Dr. Nefario, and the minions launch a rescue operation in mid-air. Gru and his allies are able to save the three girls just as the expansion of the moon engages Vector's ship hyper jump into space. The moon returns to its original size in its orbit, destroying Vector's ship and stranding him on its surface with a space helmet.
Some time later, Gru has readopted the girls and treats them as his family, and he writes them a bedtime storybook framed around his own experience. The girls perform their own ballet recital for Gru, his mother, Dr. Nefario, and the minions, with the movie ending as they all get on stage to dance.
