In 2009, Monteith was cast in the Fox series Glee. Monteith portrayed Finn Hudson.
When Glee was being cast, Monteith's agent, Elena Kirschner, submitted a video of him drumming with some pencils and Tupperware containers.
Series creator Ryan Murphy took notice of the video, but pointed out that he had to be singing, as auditioning actors for Glee with no theatrical experience were required to prove they could sing and dance as well as act.
Monteith submitted a second, musical tape, in which he sang "a cheesy '80s music video-style version" of REO Speedwagon's "Can't Fight This Feeling".
He then attended a mass audition in Los Angeles; his vocal skills were considered weak, but he later performed very well with one of Glee's casting directors, who said that his audition captured the most elusive quality of Finn's: his "naive, but not stupid, sweetness".
Monteith said of his casting process, "I was like a lot of kids, looking for something to be interested in.
Something to be passionate about. All you need is permission. Not only for Glee, but for anything in life."
Finn is the star quarterback of his high school football team, and risks alienation from his friends by joining the school's glee club.
He is a popular jock at the top of the school's social hierarchy, but when forced to join the glee club, he finds he loves it.
His storylines have seen him struggle with his decision to stay in the club, which is at the bottom of the social ladder, while he maintains his popular reputation and the respect of the other jocks.
The character must deal with his attraction to both head cheerleader Quinn Fabray (Dianna Agron) and glee club star singer Rachel Berry (Lea Michele), and his storylines increasingly focus on his relationship with them both.
Monteith felt that Finn has had to grow up a lot during his time on the show.
The actor said, "Finn started off as the stereotypical dumb jock but as the show has gone on, Finn's not dumb anymore, really, he's just a little naïve."
Early reviews of Finn from television critics were mixed; Todd VanDerWerff of The A.V. Club said that he and Michele were "both agreeable and a little desperate for an outlet" in the pilot episode. Commenting on the fifth episode of the first season, Eric Goldman of IGN wrote, "We got to see a bit of a darker side to Finn [...] it's good to see this, because up until now, Finn's been a bit too straight-laced to totally invest in."
In the second season's eighth episode, "Furt", Tim Stack of Entertainment Weekly noted "It's been a while since we've gotten some Finn focus, and I think I just missed Cory Monteith.
But I also forgot what a good, natural actor he can be." Monteith as Finn won the 2011 Teen Choice Award for Choice TV: Actor Comedy, and was nominated in the same category in 2010.
Although he was not a singer before being cast as Finn, Monteith has sung lead or joint lead on a large number of songs on the show.
In May 2010, the cast of Glee went on a two-week live tour with stops in Los Angeles, Phoenix, Chicago, and New York City.
The cast performed hits from the show and several skits between songs.
The following May, the cast went on a second tour with mostly new songs and all-new skits, performing for four weeks in the USA and Canada, and 11 days in England and Ireland.
