O’Connell was born in Los Angeles, California, on December 18, 2001. She is the daughter of teacher, actress, and screenwriter Maggie Baird, and construction worker Patrick O’Connell, who worked part-time as an actor, appearing in films like Iron Man (2008). Both her parents are amateur musicians. She is of Irish and Scottish descent. The singer’s middle name, Eilish, was originally meant to be her first name, while Pirate (proposed by her brother Finneas, four years her senior) was to be her middle name. She was conceived via in vitro fertilization. She was raised in Los Angeles’ Highland Park neighborhood.

She was raised as a vegetarian before becoming vegan in 2014.

On November 18, 2015, Eilish recorded the song “Ocean Eyes”. The track was written, mixed, and produced by Eilish’s brother, Finneas O’Connell. Finneas had written and produced “Ocean Eyes” originally for his band the Slightly’s, before realizing it would be a better fit for Eilish’s vocals. He gave it to Eilish when her dance teacher at the Revolution Dance Center (Honolulu Avenue, Los Angeles) Fred Diaz asked them to write a song for choreography and uploaded it on SoundCloud. When Eilish got a growth plate injury, it put an end to her dancing career and she turned her focus toward a recording career. A music video for “Ocean Eyes” was directed by Megan Thompson and was uploaded to Eilish’s official YouTube channel on March 24, 2016. Eilish and Finneas then released “Six Feet Under” through SoundCloud on June 23, 2016 as her second single. A homemade music video for “Six Feet Under” was released on June 30, 2016. It was directed by Eilish and edited by her mother, Maggie Baird. Justin Lubliner noticed Eilish’s talent after hearing “Ocean Eyes” and signed her to Darkroom and Interscope Records. He developed her rollout as an artist, taking inspiration from the model of hip hop artists such as Travis Scott and Chance the Rapper, not relying on one big single and focusing on creating a “persona and distinct aesthetic”. Darkroom and Interscope Records would later re-release “Six Feet Under” as a standalone single for digital download and streaming on November 17, 2016.

“Ocean Eyes” and Eilish received praise and promotion from various media outlets and marketers, including radio stations and music supervisors such as Beats 1, KCRW, BBC One, Zane Lowe, Jason Kramer, Annie Mac, and Chris Douridas. Finneas’ manager had reached out to him after he made “Ocean Eyes” to discuss Eilish’s potential. In a deal arranged by Finneas, Apple Music signed Eilish to A&R company Platoon, which helps package artists before they get a major label deal. Eilish then got a publicist, who connected her to the luxury fashion brand Chanel, and a stylist, both of whom helped shape her image. “Ocean Eyes” was re-released for digital download and streaming on November 18, 2016. A dance performance music video for the song was uploaded to Eilish’s YouTube channel on November 22, 2016.

On January 14, 2017, Eilish released an EP with four remixes by Astronomyy, Blackbear, Goldhouse and Cautious Clay for “Ocean Eyes”, and relased anohter EP for “Six Feet Under” featuring remixes by Blu J, Gazzo, Jerry Folk and Aire Atlantica. Following the success of the “Ocean Eyes” remixes, Eilish released “Bellyache” on February 24, 2017, A music video for the song was released on March 22, 2017, and was directed by Miles and AJ. Eilish later released “Bored” on March 30, 2017, as part of the soundtrack to the Netflix series 13 Reasons Why. A music video for “Bored” was later released on June 26, 2017. In March of the same month, Apple Music showcased Eilish at the South by Southwest music festival. On June 30, 2017, Eilish released “Watch”. Eilish later released another single, “Copycat”, which was released on July, 14 2017, and announced the release of her debut EP, Don’t Smile at Me. Eilish later released “Idontwannabeyouanymore” and “My Boy”. On August 11, 2017, Eilish released Don’t Smile at Me. The EP was a sleep hit, reaching number 14 on the US Billboard 200. Eilish embarked on the Don’t Smile at Me Tour throughout October 2017 in support of her EP. Eilish released “Bitches Broken Hearts” through SoundCloud on November 10, 2017.

Eilish’s team worked with Spotify, which promoted her on its most popular playlist, “Today’s Top Hits”. The Baffler described Eilish’s sound as fitting into the “streambait” genre consisting of largely “mid-tempo, melancholy pop” influenced by Lana Del Rey, whose “singing style, bleakness, and the hip-hop influenced production” shaped the aesthetic. Eilish’s commercial success expanded with her Spotify promotion. In September 2017, Apple Music named Eilish their Up Next artist, which followed with a short documentary, a live session EP and an interview with Zane Lowe on Apple Music’s radio station Beats 1. That month, the live EP titled Up Next Session: Billie Eilish was released. On December 15, 2017, Eilish released her collaboration with American rapper Vince Staples titled “&Burn”, which is a remix of Eilish’s previously released single “Watch”. It was later included on the expanded edition of Don’t Smile at Me.

Much of the media attention surrounding Eilish has revolved around her fashion style, which consists primarily of baggy, ill-fitting clothing. In 2017, Eilish stated that she likes dressing out of her comfort zone to feel like she grabs the attention of everyone around her. She tries to be “really different from a lot of people” and dresses opposite to what others wear. Aiming to “look memorable”, Eilish said that she “proved to people that [she’s] more important than they think” and likes being “kind of intimidating, so people will listen up.” In 2019, she stated: “Over time it’s kind of become a thing, ‘Billie Eilish, the creepy, weird, scary girl.’ And I don’t like that. It’s lame. I just don’t want to stay one thing.”

In February 2018, Eilish embarked on her second headlining concert tour, the Where’s My Mind Tour, which concluded in April 2018. “Bitches Broken Hearts” was re-released worldwide on March 30, 2018. For Record Store Day 2018, Eilish released “Party Favor” on a pink 7-inch vinyl, along with a cover of “Hotline Bling”, written by Canadian rapper Drake as the B-side. Eilish collaborated with American singer Khalid for the single “Lovely”, which was released on April 19, 2018, and added to the soundtrack for the second season of 13 Reasons Why. She later released “You Should See Me in a Crown”, in July 2018, In July of the same year, Eilish performed at the Mo Pop Festival. On the day of release for her single “When the Party’s Over”, Eilish was featured in Vanity Fair’s “73 Questions” rapid-fire questionnaire video series by Joe Sabia who revisited a previous interview from October 2017. The resulting video was a side-by-side time capsule of both interviews showing her growth in popularity over one year. She signed a talent contract with Next Management for fashion and beauty endorsements in October 2018. She was placed on the 2018 Forbes 30 Under 30 list in November of that year, and released the single “Come Out and Play” in November 2018, which was written for a holiday-themed Apple commercial. In early January 2019, Don’t Smile at Me reached 1 billion streams on Spotify, making her the youngest artist to top 1 billion streams on a project. That month, Eilish released “Bury a Friend” as the third single from her upcoming debut album When We All Fall Asleep, Where Do We Go?, along with “When I Was Older”, a single inspired by the 2018 film Roma, which appeared on the compilation album Music Inspired by the Film Roma. In February, Eilish partnered with YouTube for a documentary mini-series titled “A Snippet Into Billie’s Mind”. “Wish You Were Gay”, her fourth single from the album, was released on March 4, 2019,

When We All Fall Asleep, Where Do We Go? was released on March 29, 2019. Spotify launched a “multi-level campaign behind the album”, creating a multi-media playlist and “new product features” that Spotify stated “allow for vertical video content, custom assets, and editorial storylines all with the goal of creating more meaningful and engaging context for [Eilish’s] fans.” In Los Angeles, Spotify set up a “pop-up enhanced album experience”, which included different artwork and a “multi-sensory” experience of each track for fans. The album debuted at No. 1 on the Billboard 200 as well as on the UK Albums Chart, making Eilish the first artist born in the 2000s to have a No. 1 album in the United States, and the youngest female ever to have a No. 1 album in the United Kingdom. Upon the album’s debut, Eilish broke the record for most simultaneously charting Hot 100 songs by a female artist, with 14, after every song from the album, excluding “Goodbye”, charted on the Hot 100. The fifth single from the album, “Bad Guy”, was released in conjunction with the album. A remix of the song featuring Justin Bieber was released in July 2019. In August, Bad Guy peaked at No. 1 in the US, ending Lil Nas X’s record-breaking 19 weeks at No. 1 with “Old Town Road”. She is the first artist born in the 2000s and the youngest artist since Lorde (with “Royals”) to have a number-one single.

Eilish began her When We All Fall Asleep Tour at Coachella Festival in April 2019, with the tour concluding on November 17, 2019 in Mexico City. In August 2019, Eilish partnered with Apple Music for Music Lab: Remix Billie Eilish, part of Apple Stores’ Music Lab sessions during which fans deconstruct her song “You Should See Me In A Crown” and learn how to create their own remix on Apple devices and GarageBand. On September 27, 2019, Eilish announced her Where Do We Go? World Tour via her Instagram page. The tour was set to begin in Miami on March 9, 2020 and conclude in London on July 27, 2020, but had a number of dates postponed due to the COVID-19 pandemic.

On November 7, 2019, Jack White’s Third Man Records announced the label would be releasing an acoustic live album of Eilish’s performance from the record label’s Blue Room, exclusively sold on vinyl at Third Man retail locations in Nashville, Tennessee, and Detroit, Michigan. On November 13, 2019, she released her next single, “Everything I Wanted”. On November 20, 2019, Eilish was nominated for six Grammy Awards including Record of the Year and Song of the Year for “Bad Guy” as well as Album of the Year and Best New Artist. At age 17, she became the youngest artist to be nominated in all four General Field categories. In the same month, Eilish was crowned 2019’s Billboard Woman of the Year.

Eilish has wanted to direct her own music videos since she was 14 but was initially not given the opportunity due to lack of experience. In 2019, she made her directorial debut with the video for her song “Xanny”.

She is the youngest person, second person ever, and first female to win the four main Grammy categories – Best New Artist, Record of the Year, Song of the Year and Album of the Year – in the same year. In 2019, Time placed her on their inaugural “Time 100 Next” list.

According to Kenneth Womack in 2019, Eilish had “staked her claim as the reigning queen of electropop” with her debut album and “been variously called out for being precocious and the poster child for late-adolescent angst. But in truth, she’s nothing of the sort.”

In May 2019, Eilish appeared in a Calvin Klein advertisement, wherein she mentioned that she dresses in baggy clothes to prevent people from body-shaming her. In a March 2020 live show in Miami, as part of the Where Do We Go? Tour, Eilish premiered a short film entitled Not My Responsibility which addresses her experiences of body-shaming. Not My Responsibility was later uploaded to Eilish’s YouTube channel in May 2020.

In April 2019, Eilish released clothing in collaboration with Takashi Murakami, inspired by her music video for “You Should See Me in a Crown”, also directed and animated by Murakami, as well as a limited edition vinyl figure of herself from the video. Eilish also collaborated with Adobe Creative Cloud the same month for a series of advertisements as well as a social media art contest, where users would submit artwork with the hashtag “#BILLIExADOBE”.

Eilish appeared in the debut of Calvin Klein’s “I Speak My Truth In #MyCalvins” ad campaign in May 2019, as well as the Ad Council’s “Seize the Awkward” campaign, a series of PSAs targeting mental health awareness. She fronted MCM Worldwide’s fall 2019 advertising campaign in July 2019, and later that month, collaborated with Los Angeles-based clothing brand Freak City for a clothing line. Also in July 2019, she performed at a dinner hosted by Chanel on Shelter Island to celebrate the brand’s pop-up yacht club.

In August 2019, Eilish partnered with Apple to allow Apple Store customers to experiment with her song “You Should See Me in a Crown” in Music Lab sessions in its stores. Eilish’s collaboration with the clothing company Siberia Hills was met with controversy after it was revealed that the company had used plagiarized designs of fan art of the character Nozomi Tojo from Love Live!, drawn by artist Makoto Kurokawa, for Eilish’s clothing line. The brand later clarified that Eilish herself had no knowledge of the plagiarism.

Eilish is a regular advocate on social media for animal rights and veganism, and among others has criticised the dairy, wool, and mink fur industries. In 2019 she won a PETA “Best Voice for Animals” award for her activism.

On January 14, 2020, Eilish was announced as performer of the title track for the 25th installment in the James Bond film franchise, No Time to Die, written and produced with her brother. With this announcement, Eilish became the youngest artist to write and perform a James Bond theme song. The song was released as a single February 13, 2020. Shortly after, it became the second Bond theme song to top the British official charts and the first Bond theme performed by a female artist to do so. It was also Eilish’s first No. 1 single in the UK. At the 62nd Grammy Awards, she became the youngest person and first woman to win the four main Grammy categories – Best New Artist, Record of the Year, Song of the Year and Album of the Year – in the same year. During the COVID-19 pandemic, Eilish and O’Connell performed for both iHeart Media’s Living Room Concert for America, and Global Citizen’s Together at Home concert series, singing a cover of Bobby Hebb’s “Sunny” for the latter. Both virtual concerts were an effort to raise awareness and funds towards fighting the disease. On April 10, 2020, “Ilomilo” was sent to Italian contemporary hit radio stations by Universal Music Group, as When We All Fall Asleep, Where Do We Go?’s seventh and final single. On July 30, 2020, Eilish released “My Future”, her first original release since “No Time to Die”, along with an animated video. In 2020, she became the youngest person to feature on Forbes’ annual ranking of the 100 highest-paid celebrities in the world, with earnings of $53 million.

In October 2020, Eilish announced a livestream concert titled Where Do We Go? The Livestream set to air from Los Angeles on October 24 of that same year, with proceeds from the show’s merchandise raising funds to support event crew members affected by the COVID-19 pandemic. Eilish was also the winner of three Billboard Music Awards on October 24, 2020—Billboard Music Award for Top Female Artist, Billboard Music Award for Top Billboard 200 Album (When We All Fall Asleep, Where Do We Go?), and Billboard Music Award for Top New Artist—out of the 12 that she was nominated for. In that same month, she also announced a new single, entitled “Therefore I am”, which was released along with its music video on November 12, 2020.

In 2020, Eilish has also gotten involved in supporting United States voting rights. Eilish suggested that her fans pick a group working to register voters to support. In August 2020, Eilish performed at the 2020 Democratic National Convention, and announced her endorsement of Joe Biden’s presidential campaign.

As of 2020, Eilish continues to live with her parents in the Highland Park neighborhood of Los Angeles. She has revealed that she lives with Tourette syndrome and depression, and experiences synesthesia. In a 2020 radio interview, her parents revealed that they considered taking her to therapy over her childhood obsession with Justin Bieber.