The song originated from a jam session in Los Angeles, California, and was intended to be released as the lead single from the album, ultimately being replaced by "People" (2019).

Speaking to Brendan Wetmore of Paste, Healy and Daniel revealed that "The Birthday Party", specifically the whispered vocal delivery, was heavily influenced by their earlier music recorded under the monicker of Drive Like I Do.

[3] On 18 February 2020, the 1975 announced on Twitter that "The Birthday Party" would debut live on Zane Lowe's Beats 1 Radio show at 5 PM, followed by the music video one hour later.

The female voices heard in "The Birthday Party" were planned to be recorded by an actual choir, but the 1975 chose to keep Healy's distorted vocals instead, finding them amusing.

They tried several versions but were unsatisfied with all of them, going on to dismiss the chorus idea and chose to add an instrumental finale instead, inviting John Waugh to create the brass arrangements.

[21] It has an unconventional impressionist song structure,[22] with Healy delivering the lyrics in a conversational, spoken word stream of consciousness that details an internal monologue, characteristically found in country music.

[8][18][23][24] Ben Boddez of the Vancouver Weekly compared the song to the works of Father John Misty,[13] while Kyle Kohner of Riff Magazine called "The Birthday Party" a "glitch-folk dreamscape",[25] and Ryan Leas of Stereogum described it as a "deconstructed internet country ballad".

[18] Lyrically, Leas classified "The Birthday Party" as a "free-associative journey through relationships and sobriety",[18] while fellow Stereogum writer Chris DeVille noted it "explores the quest to stay pure when hard drugs and illicit sex beckon and your favorite new band has been cancelled".

[8][18][26] Paul Schrodt of Slant Magazine said the song sees "[Healy] amusingly coping with his ongoing addiction issues at a lame gathering".

[27] Barricade Magazine critic Shahin Rafikian identified underlying themes of friendship, intimacy, sociality and "admiration of life" in the track's lyrics.

[31] The singer mocks the partygoers perceived wealth ("Then drink your kombucha and buy an Ed Ruscha") and bemoans attending the gathering ("Look, the fucking state of it / I came pretty late to it").

Deeming it the best track on the album, Rachel Hunt of The Diamondback praised the song's upbeat, witty and catchy nature, saying listeners "get an in-depth look into Matty Healy's inner dialogue concerning his love-hate relationship with fame and his shallow interactions with people".

[13] Callie Ahlgrim and Courteney Larocca of Insider deemed "The Birthday Party" an album highlight, praising the "airy, chilled-out" production and sharp, perceptive lyrics.

[8] Similarly, Caitlyn McGonigal of Ascribe Magazine praised the song's sonic experimentation and the band's versatility, saying: "If there's a way to blend sounds together, they'll give it a try; if there isn't, then they'll invent a way to do it.

"[36] Ali Shutler and Stephen Ackroyd of Dork called the song genuine and sincere, saying it gives Notes on a Conditional Form a "warm, beating heart".

[39] Leas called the song a "blearier-eyed update" of "Sincerity Is Scary" (2018), saying it contains more nuanced soundscapes than previous releases, "coming together in a kind of wan, late-night document of listless twentysomething life".

[10] Rolling Stone writer Claire Shaffer gave the song a negative review, calling the "Pinegrove" line bizarre and awkward, while also criticising the length, saying: "did we really need a five-minute track to remind us that small talk at parties can be boring?

"[31] Similarly, Lizzie Manno of Paste called the line "cynical" and noted the 1975 failing to take a stance on the controversy, using it to show their knowledge of pop culture instead.

Club, Annie Zaleski said several songs, including "The Birthday Party", contain topics which deserve deeper thought, specifically Healy's references to sobriety.

[32] In a separate "Ask A Music Critic" column for Uproxx, Steven Hyden gave the song a scathing review, calling it "a pale imitation of the emo-leaning folk of Pinegrove's own records, utterly weak and directionless".

[43] He derided the "Pinegrove" line, labelling it an attempt to fortify a brand image that portrayed the band as clever and relevant, "more akin to personal identity curation than (exceedingly half-baked) commentary".

[48] Discussing his collaboration with the band, Ditto said: "It was truly inspiring to work with [t]he 1975 on this project, combining digital craft with true emotion and a subversive and multilayered narrative."

[49] Speaking with Alex Peters of Dazed, Healy said: "[...] you'll see memes that actually originate from really dark, deep places, the underbelly of the internet but are now fodder for the masses.

"[50] The band wanted to explore where memes such as Lil Miquela would go to relax, resulting in the idea of a digital detox centre located outside in nature.

A neon doorway appears, similar to the "box" used for the artwork on the 1975's EPs, their eponymous debut studio album (2013) and I Like It When You Sleep, for You Are So Beautiful yet So Unaware of It, revealing a new world populated by "meme-people".

[52][53][54] In the forest, an incel Virgin rapidly nails posters to the trees that read "looking for goth gf" above a photo of the Danny Phantom character Sam Manson.

Scenes of the Virgin finding his "goth gf" and Healy kissing a clone of himself are shown and the remaining "meme-people" collapse in a circle as the band performs.

[52][53][54] Koltan Greenwood of Alternative Press called the music video captivating and a "wild ride", observing a dystopian theme that deals with the divisive effects of social media: isolation and narcissism.

[58] Consequence of Sound writer Wren Graves gave the video a positive review, calling it "certainly impressive, even if it lingers in the Uncanny valley".