The song was written by band members Matty Healy, George Daniel, Adam Hann, Ross MacDonald, with the first two handling the production alongside Mike Crossey.

The video received positive reviews from critics, who highlighted the cinematic quality, introspective style and twist ending, with several comparing it to the work of filmmaker David Lynch and the film Fight Club (1999).

In addition to appearing in several films and television shows, such as 13 Reasons Why and The Edge of Seventeen (2016), the song has been covered by several artists including Charlie Puth, Vérité and Lorde, with the latter citing it as a significant influence on her second studio album, Melodrama (2017).

[8][9][10][11] The song has a length of four minutes and fifty-seven seconds (4:57) and was written by the 1975 members George Daniel, Matty Healy, Adam Hann and Ross MacDonald, while the former two handled the production alongside Mike Crossey.

[14] "Somebody Else" has a sparse 1980s-style production composed of a "bounc[ing]" synth line, heavy reverb, expansive atmospherics,[16] whirling synthesiser washes, a disco-influenced bass, a kick drum,[17] 808 percussion and techno beats.

[18][19][20] The song also contains elements of house,[21] chillwave,[22] electro,[23] funk, neo-soul,[24] electronica,[25] dance,[26] electropop,[27] alternative pop,[28] new wave,[29] yacht rock and "digitized" soul.

[31] Pitchfork's Brad Nelson noted that, unlike the 1975's prior work, the band embodies "something less defined and more introspective" in the song, writing it explores feelings of confusion which one would normally suppress.

[32] Writing for Billboard, Rania Afitos felt the song moves through several stages of heartbreak, beginning with melancholy and grief before capturing Healy's "inevitable bitterness".

[33] Tom Connick of DIY characterised the production of "Somebody Else" as gentle and "soft-of-touch" while writing that the lyrics see Healy "finally [laying] himself bare in the emotional sense, rather than just whipping off his top and skipping about".

[37][38][39] Nelson observed a "swerve" to the opening synths that sonically embodies post-breakup ambivalence, noting "a damp echo to the atmosphere that makes every instrument sound slightly hazy and drunk".

"[17] Characterised by a change in tempo,[40] slower synths and distorted vocals, the song's bridge sees the singer's heartbreak shifting to bitterness around intimacy, as he exclaims: "Get someone you love?

[43] Regarding the song's bridge, Jennifer Irving of Consequence interpreted the lyrics as a commentary on love in the 21st century, representing society's inability to make time for intimacy.

[31] Describing "Somebody Else" as a "timeless" ballad, Amit Vaidya of Rolling Stone India deemed it the best song of the 1975's career; she gave specific praise to the successful emulation of a 1980s-style sound: "If I placed this single with my Top 30 of 1988, it would fit it so perfectly, no one would know it didn’t come out 30 plus years ago!

[58] Stroud declared it the best song on I Like It When You Sleep, for You Are So Beautiful yet So Unaware of It; he commended the track's lyrics for representing an "obsession" that sees Healy "teetering toward a full-on psychosexual breakdown".

[18] Writing for NME, Connick deemed "Somebody Else" one of the band's best songs and called it a "heartbreak hit like few others", praising the songwriting for exploring tropes of love, sex, death and drugs without succumbing to "longstanding cliches".

[60] Describing the track as a "synth-laden masterpiece", Callie Alghrim of Insider commended its lyrical elegance, relatability and portrayal of nostalgia, misery, guilt, self-importance and betrayal, saying: "There is no other song in existence that evokes the same ultra-specific, exquisite emotion as 'Somebody Else.

'"[61] Writing for The Observer, Kitty Empire said "Somebody Else" is a "gem",[62] while Renowned for Sound writer Jessica Thomas opined the song radiates "soulful passion, with deep, personal significance".

The black and white vignette opens with Healy entering a grim hotel room, reminiscent of a retro TV show set, where a woman who never moves is sitting on the couch.

The singer performs several menial tasks in a lethargic manner; he washes away clown makeup from his face, takes off his suit jacket and shirt, ties his shoes and studies himself in a mirror.

[99][103] The singer steals a pair of sunglasses from a fellow patron before performing on stage, where his compounding loneliness leads to him hallucinating seeing his former lover in a group of hecklers.

In addition to declaring it one of the band's most experimental visuals, Sharples praised the vignette for "speak[ing] to how, when depressed, going about life's basic functions feels like an immense effort".

[104] Writing for MTV News, Madeline Roth called the visual colourful and "ominous", noting that the twist ending is "totally unexpected" and viewers "have to see [it] to believe [it]".

[102] Writing for Euphoria Magazine, Christine Nguyen praised the visual's cinematic quality, production and Healy's "striking and convincing" acting, comparing the music video to Lynch and Fight Club (1999).

[107] Jisselle Fernandez of B-Sides said the accompanying music video does "Somebody Else" "justice",[108] while Josephs felt it matches the song's "moodiness", writing: "The wearing-a-leather-jacket-in-the-night life ain't easy.

[109] Deeming the music visual odd and strange, The Fader writer Ben Danridge-Lemco said it is both an examination of narcissism and a representation of Healy's journey to find himself, writing the track itself functions as his soundtrack.

[110] Peter Helman of Stereogum commented that the visual is similar to Father John Misty's "The Night Josh Tillman Came To Our Apartment" (2015) and Young Thug's "Best Friend" (2015), deeming it "another solid entry into the pantheon of 'musician fucks himself' music videos".

[121][122] In June 2017, Holden accidentally played his vinyl copy of I Like It When You Sleep, for You Are So Beautiful yet So Unaware of It at double speed, discovering the song sounds similar to the work of Scottish synth-pop group Chvrches.

In the publication's list of Gray's Top Five Favourite Covers, Soundigest ranked his performance of the track at number one; Courtney Gould commended the video's lighting and his vocals for "highlight[ing] the dynamic details that make this song so special".

[133] Korean-New Zealand singer Rosé, a member of K-pop girl group Blackpink, performed the track as part of an Instagram Live mini-concert on 17 May 2020, closing out the show.

[50][33][135] Johnson II ranked the track at number 17 on Paste's list of the 1975's essential songs and said its lyrics "highlight the splintered emotions that make breakups a process".