She made her acting debut as Summer Hathaway in the film School of Rock (2003), and her breakthrough role was Megan Parker on the Nickelodeon sitcom Drake & Josh (2004–2007).

[13] Cosgrove's first television appearance was in 2001 when she provided the voice of young Lana Lang in the pilot episode of Smallville.

In the movie, she played Summer Hathaway, a young girl with great ambition and discipline who finds herself adjusting to the free-spirited nature of her new music teacher (Jack Black).

In 2005, Cosgrove was awarded the role of Munch in the Cartoon Network film Here Comes Peter Cottontail: The Movie.

In the film, Cosgrove portrays a female mouse who is rescued from a hawk by Junior and Flutter and who goes on to join them on their adventure.

Creator Dan Schneider tailored iCarly around the interest young people have in the internet; viewers could submit their own videos and be included in the sitcom.

[14] Her debut as a recording artist began with the iCarly theme song "Leave It All to Me",[28] which featured Drake Bell and was released as a single on December 2, 2007.

[29] In June 2008, Columbia Records released the iCarly soundtrack, which featured four songs performed by Cosgrove and debuted at number one on the Billboard Kid Albums chart.

[39] Cosgrove also voiced Margo in the Universal Studios animated feature Despicable Me, released in July 2010.

In 2010, Cosgrove worked with songwriters The Matrix, Dr. Luke, Max Martin,[37] Leah Haywood and Daniel James for her debut studio album, Sparks Fly.

"Kissin U" was released as the sole single from Sparks Fly and premiered on Ryan Seacrest's radio show on March 12, 2010.

[40] "Kissin U" became Cosgrove's best-selling single release, peaking at number 54 on the Billboard Hot 100 and being certified gold.

On February 15, 2013, Deadline reported that Cosgrove would star in Girlfriend in a Coma, a television series written by Liz Brixius for NBC and adapted from the novel of the same title by Douglas Coupland.

[52] In 2013, she appeared in the animated short films Training Wheels as Margo and Gru's Girls as Savana.

[53][54] In 2014, Cosgrove performed voice work in the animated film A Mouse Tale, which was released on February 10, 2015.

[55] Cosgrove also starred in the horror film The Intruders with Austin Butler, portraying the role of Rose Halshford.

[59] Since 2019, she has been the host of Mission Unstoppable with Miranda Cosgrove, a show which airs on CBS[60] and earned the actress a Daytime Emmy Award nomination in 2020.

[62] She reprised her role as Carly Shay in an iCarly revival, which premiered on Paramount+ in June 2021, and ran for three seasons until July 2023.

[69] Cosgrove had a starring role in the comedy film Drugstore June, which earned a limited theatrical release in February 2024.

"[73] While Mother of the Bride received mixed reviews, Amy Amatangelo of Paste believed Cosgrove "shines" in the film's emotional moments,[74] and Courtney Howard of Variety called her performance "nuanced" and "thoughtful".

"[73] Cosgrove was chosen by Common Sense Media as the role model of 2011, being the youngest artist honored at the time.

[80][81] In the 2012 edition of the Guinness World Records, Cosgrove was listed as the highest paid child actress.

[97] In 2014, Cosgrove was granted a restraining order from a Los Angeles court against a stalker who had allegedly followed her, sent her unsolicited gifts and threatened suicide.