Cotton began her presenting career aged 16 with early morning children's show Diggit, after attending Haydon secondary school in Pinner, NW london until 2004. She went on to front children's programmes The Saturday Show, Finger Tips, which allowed her to show off her artistic skills, and Smile, as well as participate in the celebrity charity singing challenge Comic Relief Does Fame Academy, from which she was the second person to be voted off. In 2003 she started presenting Top Of The Pops Saturday, graduating to become a regular Top Of The Pops presenter the following year. She also narrates the popular Serious… documentary strand. In July 2005 she made her career highlight to date, presenting Live8 in Hyde Park, London, where she was chatted up by Robbie Williams.
She is currently one of the regular presenters of the BBC's annual Children in Need telethon, where she often participates in magic tricks and illusions. During the 2005 telethon, she became the first British celebrity to take part in a new version of the famous sawing a woman in half illusion. In this illusion, called the Impossible Sawing, she was sawed in half by magician Scott Penrose without any coverings over her.