The show centers on Timmy Turner, a 10-year-old boy who is neglected by his parents and tortured by his babysitter Vicky. One day, he is granted two fairy godparents, Cosmo and Wanda, who grant his every wish to improve his miserable life. However, these wishes are guaranteed to inadvertently cause a series of technical problems that Timmy must fix. In the beginning of the series, Timmy's babysitter Vicky was the main antagonist. As the series progressed, more villains were included. For example, his teacher, Mr. Crocker, firmly believes in fairy godparents and has been searching for them a very long time, correctly suspecting that Timmy has fairy godparents. He is dangerous to Timmy because, according to "Da Rules", a large rule book which is capable of defining what children can and cannot wish for and how fairy godparents must behave, no one else can know about his fairy godparents and they will be taken away if this happens (although he doesn't remember, Cosmo and Wanda once used to be Crocker's fairy godparents, as this rule does not apply to people who currently have their own or once had fairy godparents).
At his school, Timmy is often bullied by Francis, a vicious boy who claims to be the toughest student in school, but reveals to Timmy that he only takes out his anger on him because of his rough home life and abusive parents. Jorgen Von Strangle, the enormous and tough head fairy with an , similar to that of , personally dislikes Timmy and his fairies at first, but at times he has to assist them in fixing their problems.
Later in the series, Timmy wished that Cosmo and Wanda would have a baby, whom they later named Poof. More recently, Timmy got a pet fairy dog named Sparky. Also introduced is the premise that for every fairy, there is also an anti-fairy. The anti-fairies are similar to the real ones, but with opposite personalities and character traits. For example, Anti-Cosmo is intelligent and speaks with an English accent while real Cosmo is dim-witted. Similarly, Anti-Wanda is also dim-witted and speaks with a Southern American accent while real Wanda is intelligent. When Poof was born, his anti-fairy was created. Anti-Poof's name is Foop (Poof spelled backwards). While Poof is spherical, Foop is shaped like a cube. Foop's goal in life is to cause mayhem and destroy his nemesis Poof.
In season 10, Timmy learns that due to a shortage of available fairies, he must now share Cosmo and Wanda with his neighbor, Chloe, who is essentially his polar opposite. She loves sharing, animals, and everything ecologically friendly.
