Miranda Cosgrove was born in Los Angeles, California. When she was about 3 years old, she was singing and dancing in a restaurant called "Taste of LA". A talent agent was impressed with her singing and dancing skills so he signed her up for his talent agency, leading to a career in advertising soon after, as well as other roles and shows. She began homeschooling after she finished elementary school, at Maude Price Elementary School in Downey, California, and then enrolled in an online school program which she has been doing since 2006.

The starting point of her career was when she got roles in ads for McDonald's & Burger King. Later on she auditioned for roles in several movies and TV series. Her audition for the role of a student named Summer Hathaway in the film School of Rock starring Jack Blackwas successful and she began filming in 2002. School of Rock went on to be a big hit. During School of Rock's premiere, news arrived that a pilot for a TV show she participated in had been green-lit, and that she would be playing the part of Megan Parker, the scheming sister of Drake, in the hit show Drake & Josh. She also had a role in the 2005 film Yours, Mine, and Ours. Her character, Joni North, was the sister of Dylan North (Drake Bell, who is her co-star in Drake & Josh. In 2006, she had a minor role in the film Keeping Up with the Steins as Karan Sussman. Also in 2006, a feature-length episode of Drake & Josh called Drake & Josh Go Hollywood had her again playing the role of Megan Parker, as well as in the second feature-length episode Drake & Josh: Really Big Shrimp, which aired August 3, 2007. In the same year, production on Drake & Josh ceased. Cosgrove has guest starred in a number of Nickelodeon television shows, including All That, Zoey 101, Just Jordan and Unfabulous.

Cosgrove currently stars in the role of Carly Shay in the Nickelodeon series iCarly, which debuted on September 8, 2007. She performs the show's theme song with backing vocals by Drake Bell Co-starring is Jerry Trainor, who played Crazy Steve on Drake & Josh. Her newest song, Stay My Baby, was released on Facebook and Myspace. It was a cover of Amy Diamond's song.

On June 10, 2008 she released an album called iCarly - Music From and Inspired by the Hit TV Show. Her single "Leave It All To Me" had its music video premiere on Nickelodeon's TEENick on May 24, after an episode of iCarly.