He rose to fame for his role as Ron Weasley in the Harry Potter film series, for which he was cast at age eleven, having previously acted only in school plays and his local theatre group.

After the Harry Potter series concluded, he appeared in the films Into the White (2012), Charlie Countryman (2013), CBGB (2013), Moonwalkers (2015), and Knock at the Cabin (2023).

[9] Grint, a fan of the book series, chose to audition for the role of Ron Weasley, one of Harry Potter's best friends at Hogwarts.

[10] In August 2000, Daniel Radcliffe, Emma Watson, and Grint were selected to play Harry, Hermione Granger, and Ron.

The film sees all three of its lead characters hover on the brink of adolescence, "and while they look braver and more capable than before, the dangers they face seem far more grave and their vulnerability more intense.

"[21] Alfonso Cuarón took over direction for Prisoner of Azkaban, which remains the lowest-grossing Harry Potter film with US$795 million in revenue.

[25] Goblet of Fire is one of the series' best-reviewed instalments, and is noted for its characters' maturity and sophistication, darker and more complex plotline, and the quality of the screenplay and lead actors' performances.

[25] Grint and his Harry Potter co-stars left imprints of their hands, feet and wands in front of Grauman's Chinese Theater in Hollywood.

[29] On 15 July 2009, the series' sixth instalment, Harry Potter and the Half-Blood Prince, was released and again set box office records.

[15] It is also one of the most positively reviewed Harry Potter films, with critics praising its "emotionally satisfying" story, direction, cinematography, visual design and music.

[32][33] Grint observed a change in Ron in this entry, pointing out that his once insecure, often overshadowed character started to become more secure and even began to show a dark side.

[40] Although he disliked the film, Joe Morgenstern of The Wall Street Journal wrote that "Grint has grown up to be a skilful actor who knows the value of a slow burn".

She said that there were seven Harry Potter film series cast members whom she called "The Big Seven"; Grint was one of them, with Daniel Radcliffe, Emma Watson, Tom Felton, Matthew Lewis, Evanna Lynch and Bonnie Wright.

[48] In 2002, Grint starred in his first non-Harry Potter film, Thunderpants, which revolves around Patrick (played by Bruce Cook) whose remarkable capacity for flatulence scores him a job as an astronaut.

Most critics who did take notice of it did not respond well to it, with one writing: "This film should be shown in prisons so that inmates have a good reason to never return.

"[49] Grint also appeared in Driving Lessons, a comedy drama released in 2006, starring opposite Julie Walters.

[He] displays an innate naturalness mixed with personal charisma that turn a potentially pathetic Christian freak into a humorous, thoroughly likable – if more than a little awkward – young man".

[52] Jonathan Lynn directed Grint in Wild Target, a 2010 comedy thriller, where he starred with Emily Blunt and Bill Nighy.

[53] It was a commercial failure, earning only US$3.4 million,[54] and garnered mostly negative reviews in the media, which criticised it for dishonouring the original film and wasting the comedic potential of its cast.

[57] In March 2011, he was cast as the lead character in the small-budget anti-war Norwegian film Into the White, directed by Petter Næss.

It is based on a real incident that took place on 27 April 1940, when German Luftwaffe pilot Horst Schopis's bomber was shot down at Grotli by a Royal Navy Fleet Air Arm Blackburn Skua, which then crash-landed.

[59] In August 2011, Grint did a photo shoot with his friend and Harry Potter co-star Tom Felton in Los Angeles for the autumn/winter collection of the fashion label Band of Outsiders.

[60] In September 2011, it was announced that Grint would voice a character in the film adaptation of Postman Pat along with David Tennant, Stephen Mangan and Jim Broadbent; it was released in May 2014.

[62] In March 2012, the "Visit Britain" TV ad was released, featuring Grint alongside Julie Walters, Michelle Dockery and Stephen Fry, promoting holidaying at home in the UK.

[67] On 13 February 2013, The Hollywood Reporter's Live Feed announced that Grint would star in a television pilot for CBS called Super Clyde.

The play, which also starred Brendan Coyle, Ben Whishaw and Daniel Mays, was based on real-life events, and ran from 26 October 2013 to 8 February 2014 at the Harold Pinter Theatre in London.

[70] In September 2013, The Hollywood Reporter confirmed that Grint would star in an adaptation of Macbeth called Enemy of Man, also featuring Sean Bean, Charles Dance, Jason Flemyng, James D'Arcy, Neil Maskell and Joe Gilgun, and directed by Vincent Regan.

[78] Grint starred in the 2022 Netflix anthology series Guillermo del Toro's Cabinet of Curiosities and in M. Night Shyamalan's 2023 thriller film Knock at the Cabin.

[85][86][87] He took part in the 2012 Summer Olympics torch relay, carrying the flame through Hendon in northwest London to outside Middlesex University.

He participated in the Wacky Rally in 2010 with James and Oliver Phelps, which raised money for Britain's Royal National Lifeboat Institution.