Reid first began his music career as a drummer, with his first appearance on record being with the Cincinnati funk rock outfit Pure Essence. Pure Essence released one solitary 45 in the mid-1970s. They later appeared on local FM rock radio station WEBN's second annual LP compilation, but the group was renamed 'Essence'. Reid would experience more mainstream success when he became a member of the 1980s R&B band The Deele, best known for their 1988 hit "Two Occasions", a song on their third album Eyes of a Stranger. The band had broken up before the success of the single, then reunited to promote "Two Occasions" as it rose up the charts under Dick Griffey's Solar Records. The song peaked at number 10 on the Billboard Hot 100.
1989–2004: LaFace Records and Arista years
After The Deele disbanded, Reid and bandmate Kenneth "Babyface" Edmonds founded LaFace in 1989 through a joint venture with Arista Records, with funding from Arista Records creator Clive Davis. The label soon became one of the premiere destinations for popular African-American entertainers who created Black Pop music that was easily accessible to both Urban and Top 40 radio formats. Reid signed 14-year-old Usher to the label, whose six album releases have sold 65 million units worldwide. Other popular acts on the label during its peak include Toni Braxton, TLC, and Outkast. Both TLC and Toni Braxton went on to sell more than 65 million records each. Initially headquartered in Atlanta, the label played a significant role in developing the city's music industry.
- Hitco Publishing Group
Reid formed the Hitco Publishing Group in 1996, as a joint venture with Windswept Music. While starting up Hitco, Reid, looking to connect to a new market of producers, songwriters and talent, hired Shakir Stewart whom he saw as someone with "a finger on the pulse of the next generation of hot producers in the Atlanta music scene". Shakir's first job in the music industry was as a creative executive at Hitco; he went on to become a senior vice president at Island Def Jam Music Group.
"The most vital lesson [Reid has] learned from 22 years working at record companies? 'That you keep the doors open and the lights on and a star will walk in,' he says. 'I learned to stay in business. People are still buying music, dancing to it and dressing like it. They're using it to sell cars and CoverGirl makeup, so we sell product lines with our artists. The popularity of music is at an all-time high. How we monetize it is sometimes a moving target.'"
L.A. Reid, regarding the challenge in marketing current music artists, as quoted in The Hollywood Reporter, February 9, 2011.
In May 2000, Edmonds and Reid sold their remaining 50% stake in LaFace to parent company BMG. The label became an imprint of Arista Records, with Arista taking on sales, marketing, and promotional duties for its acts. At this time, Reid also succeeded his mentor Clive Davis as president of Arista Records.
In 2000, LaFace was merged into Arista Records with Reid being promoted to president and CEO of Arista Records. In 1997 Reid was accepted to the Harvard Business School Advanced Management Program in preparation to become CEO of Arista Records. In 2000. Reid signed his first unknown artist, pop/rocker Avril Lavigne, to Arista. Her debut album Let Go sold 6 million copies in the United States. As president of Arista Records, Reid signed artists such as P!nk (whose November 2001 album Missundaztood sold 5 million copies in the US) and Ciara (whose September 2004 debut album Goodies sold 3 million copies in the US).
Under Reid's tenure at Arista, Usher (whom Reid originally signed at LaFace) completed production on his multi-platinum hit 2004 album Confessions, which went on to spawn 4 #1 hit singles and sell 10 million copies in the United States alone. Outkast's Speakerboxxx/The Love Below sold more than 10 million copies and won a Grammy Award for Album of the year.
2004–2012: Island Def Jam Music Group and The X Factor
Following the merger of Sony and BMG, L.A. Reid was released from his contract at Arista in 2004 and became the chairman and CEO of The Island Def Jam Music Group in February 2004. Reid is noted for bringing Mariah Carey's career back to prominence with her multi-platinum 2005 album The Emancipation of Mimi after her career had stalled from 2001 to 2003 with less than stellar sales and general lack of public interest for her two previous projects, Glitter and Charmbracelet.
Reid also played a role in the successes of artists such Kanye West, Rihanna, Bon Jovi, and Justin Bieber and was credited for the musical comeback of Jennifer Lopez with her 2011 album Love?. Reid stepped down as Chairman/CEO of Island Def Jam in March 2011.
In early 2011 Reid became a judge on the U.S. version of the British television singing competition The X Factor, alongside its creator and former American Idol judge Simon Cowell, 80s pop star Paula Abdul and former Pussycat Dolls singer Nicole Scherzinger, who replaced British recording artist Cheryl Cole.
Reid was assigned the Boys category throughout the competition, aided by friend and singer Rihanna at the Judges' Houses stage of the competition in The Hamptons. His final four acts were Marcus Canty, Chris Rene, Astro and Phillip Lomax. Lomax was eliminated on week one of the Live Shows, with Astro being eliminated on week six. Marcus Canty came fourth in the competition and was eliminated by the public vote in the semi-final (week eight). Chris Rene was Reid's most successful act who came third overall in the competition, bested by Josh Krajcik (who was mentored by Nicole Scherzinger) in second place and Melanie Amaro (mentored by Simon Cowell) who won the show. After the season ended, Reid worked with Astro, Marcus Canty and Chris Rene on their music careers.
In July 2011, Reid became the chairman and CEO of Epic Records. The label's roster included various former Jive Records artists.
In September 2012, Reid returned for The X Factor's second season along with Simon Cowell, while Nicole Scherzinger and Paula Abdul were axed from the panel, along with Season 1 host Steve Jones. Joining the judging panel were new judges Britney Spears and Demi Lovato, while Khloé Kardashian and Mario Lopez replaced Jones as co-hosts. Reid's team of finalists in the "over 25's" including Tate Stevens, the winner of the season.
Reid announced in December 2012 that he would not return for the third season in 2013.
2013–present: Memoir, Xscape album, revival of Hitco
One of the projects that Reid embarked on following his stint on The X Factor, was remaking Michael Jackson songs after his death with the album Xscape, released May 2014. Reid went through 40 years of tracks catalogued by the Jackson estate, and eight tracks of Jackson vocals set to new music from Timbaland and J-Roc, Rodney Jerkins, Stargate and John McClain, the former A&M Records executive who is co-executor of the Jackson estate with John Branca. The originals they worked with were recorded by Michael Jackson from 1983 to 1999, the period just after Thriller and before Invincible. Xscape earned Gold certification.
In 2016, Reid published the memoir Sing to Me: My Story of Making Music, Finding Magic, and Searching for Who's Next. The book received favorable reviews. Soul Train wrote: "In Sing to Me: My Story of Making Music, Finding Magic, and Searching for Who’s Next, his memoir written with Joel Selvin, Reid vividly takes readers on a musical journey via fascinating stories and rare photos that chronicle his modest beginnings as a young musician in Cincinnati, to his storied and adventurous path to becoming one of the most successful music executives in history.
Under Reid, Epic had four albums debut at #1: Future, DJ Khaled, Travis Scott, and the final album from A Tribe Called Quest. On March 3, 2017 Future became the only artist on the Billboard charts to release back-to-back albums that debuted at #1. 
In May 2017, it was announced that Reid would exit his post at Epic Records following an accusation of sexual harassment. In response Reid stated: “I’m proud of my track record promoting, supporting and uplifting women at every company I’ve ever run. That notwithstanding, if I have ever said anything capable of being misinterpreted, I apologize unreservedly.”
While at Epic, Reid established the label as a hub for hip-hop acts such as Future, Travis Scott, DJ Khaled, and had significant success with pop artists including Meghan Trainor and Fifth Harmony. During his tenure, Epic grew its market share to 3.63 percent, up from 2.56 percent when he took over in 2011.
In 2018, Reid became founder and co-chairman of Hitco Entertainment, LLC with Charles Goldstuck, the former Chairman and CEO of TouchTunes Interactive Networks. The new music and entertainment company launched in January 2018, has offices in Los Angeles and Atlanta and has signed a number of acts including Outkast's Big Boi.    In April 2018 Empire, the San Francisco-based independent music company founded by Ghazi Shami, announced that it will provide distribution services to Hitco for their first new album release for Big Boi.