[2] At the beginning of the third season, Blaine transfers to McKinley High and joins New Directions; concurrently, Criss was promoted from recurring guest star to the show's main cast.

His first, a cover version of "Teenage Dream" by Katy Perry, became the fastest-selling Glee single, reached number eight on the Billboard Hot 100, and was certified gold in the U.S.[4][5] Tracks by the Warblers have sold over 1.3 million copies.

While the Blaine–Kurt ("Klaine") relationship has been met with acclaim, an episode storyline in which Blaine questioned his sexuality attracted negative reviews for undermining his previous characterization as a confident gay teenager.

[15] In the first episode of the third season, "The Purple Piano Project", Blaine transfers to McKinley High at the beginning of his junior year to be closer to Kurt, who is a senior, and joins New Directions.

[23] The two patch things up, the glee club wins at Nationals, and the pair is still a couple at the end of the school year, though Blaine is still uneasy about the prolonged physical separation facing them.

[24] In the first episode of the fourth season, "The New Rachel", Blaine becomes the lead singer of New Directions and successfully prompts Kurt to follow his New York City dreams.

[34] Blaine remains determined, however, and while shopping for a ring, he meets Jan (Patty Duke), a lesbian jeweler who has been with her partner Liz (Meredith Baxter) for over thirty years.

In "The Hurt Locker, Part Two", Sue, who "ships Klaine" and is desperate for Kurt and Blaine to reunite, locks them both in a fake elevator and refuses to let them leave until they kiss.

Dalton Academy burns down in "The Rise and Fall of Sue Sylvester", and the Warblers who transfer to McKinley are accepted into New Directions, with Blaine joining Rachel and Kurt as the coaches of the combined glee club.

The episode jumps ahead to 2020, and Blaine and Kurt are shown to be actors and a celebrity married couple; they also visit schools to entertain and talk about acceptance.

[37] Criss made several audition videos for Glee, of which he posted only one to the social networking website MySpace where he sang a cover of Bill Withers' song "Lean on Me".

[40] His original character description was: "a cute and charismatic gay student from a rival Glee club named the Dalton Academy Warblers—will maintain a strictly platonic friendship with McKinley High's most out and proud pupil.

"[3] Talk show host and media personality Ellen DeGeneres deemed Blaine "a very confident gay teen, which is something you don't see much on television.

"[55] Based on the characters' chemistry and the "immediate outcry" from fans who wanted to see them as a couple, Murphy decided to have Blaine become Kurt's love interest.

[75] Blaine also led on "Silly Love Songs" by Wings,[76] and Maroon 5's "Misery",[77] which reached 45 and 52 respectively in the U.S.,[73][78] and Pink's "Raise Your Glass", which peaked at number 30 in Australia.

[77][79] Blaine duetted with Kurt on Frank Loesser's "Baby, It's Cold Outside", which was included on Glee: The Music, The Christmas Album and reached number 53 in Canada.

[78][86] In an April 2011 interview, Criss stated that he did not feel established enough within the cast to make song suggestions, but had mentioned liking "Animal" to Murphy, who included it in a script soon thereafter.

"[67] In the first episode of season three of Glee, "The Purple Piano Project", Blaine sings "It's Not Unusual" by Tom Jones when he transfers to McKinley and quits the Warblers for New Directions.

After successfully auditioning later in the season for the school's production of West Side Story with "Something's Coming" from the musical, he sings "Tonight" in rehearsal and "One Hand, One Heart" in performance, both with his co-star Rachel.

Futterman wrote that Blaine's "slick showmanship" made him a "natural for lead vocals",[89] and TVLine's Michael Slezak called it "the best use of Darren Criss' voice on Glee in quite some time" and gave it an "A−".

Crystal Bell of HuffPost TV called it the "highlight of the episode", and it was Hankinson's favorite performance: "Bomer and Criss did a fantastic job bringing it to life".

[51] Entertainment Weekly named him one of the breakout stars of 2010, with the comment: "It took about 2 minutes and 11 seconds on Glee for Darren Criss to turn into a bona fide Gleek phenomenon.

Club also criticised the storyline, which, she wrote, "seemed like it might be an interesting, complicated look at teenage sexuality and how it can seem formed but might be more fluid than most teens would give it credit for, then lost its nerve and took the easy way out.

"[109] Entertainment Weekly's Mandi Bierly was so impressed with the scene that she was initially concerned it may be a dream sequence, "because we don't get romantic, unapologetic first kisses like that between young gay characters on network TV."

She called the kiss scene a "sweet, real and, shockingly, un-hyped moment", and praised Criss and Colfer for "handl[ing] it with dignity and honesty".

[112] While Lesley Goldberg of The Hollywood Reporter was pleased Blaine's season three transfer to McKinley in the first episode increased Criss' screen time with Colfer and the New Directions cast, she stated that the move "screams of co-dependency.

"[113] In contrast, Entertainment Weekly's Abby West found it romantic, and noted: "Blaine and Kurt, with their budding love and witty, pseudo-urbane ways, are my favorite couple to watch.

VanDerWerff wrote that Blaine "seems to have simultaneously gotten younger and had a complete personality transplant over the summer", Billboard's Rae Votta noted "the continuity-bending plot point that he's somehow a Junior and not a Senior like his boyfriend", and Samantha Urban of The Dallas Morning News allowed her exasperation to show: "Oh really, Glee?

[121] Discussing public response to his character, Criss stated that he particularly enjoyed comments from "people from parts of the world who are maybe not as exposed to certain ideologies", but had reconsidered their stance on relationships and human rights as a result of the Blaine–Kurt storyline.

He called this response "phenomenal", and said: "I was a straight kid growing up in a very gay community and it's something that I've had to watch so many friends have to struggle with and have no place to go to identify in kind of a grander media culture.