In 2015, The group released their debut studio album Reflection, which was certified gold by the Recording Industry Association of America (RIAA).

[2] It spawned the singles "Boss", "Sledgehammer" and "Worth It"; the latter of which was certified triple platinum by RIAA, and reached the top ten in thirteen countries.

In 2012, Ally Brooke, Camila Cabello, Normani Kordei, Dinah Jane and Lauren Jauregui auditioned as soloists on the second season of the American televised singing competition The X Factor.

[17] Thereafter, Lylas changed their name to 1432 (a colloquial term for I Love You Too), which was announced on the first live show on October 31, during which 1432 performed "We Are Never Ever Getting Back Together" by Taylor Swift.

During the first live results show on November 1, 1432 performed "Skyscraper" by Demi Lovato in a sing-off with three-piece girl group Sister C. Cowell decided to send 1432 through to the Top 12 and announced that they would be renamed via the viewers online.

[21][22] Three of their covers received public praise from the original artists, including Ed Sheeran, Ariana Grande and Mikky Ekko.

[34] Throughout July and August 2013, Fifth Harmony performed at various shopping malls across the United States in a promotional tour titled "Harmonize America".

[47] The album's lead single, "Boss", was released on July 7, 2014, peaked at number 43 on the Billboard Hot 100 chart with first-week sales of 75,000, and received a platinum certification by the United States for selling a million digital downloads and streams combined.

[48][33] The second single from Reflection, the Meghan Trainor-penned "Sledgehammer", was released on October 28, 2014, and went on to become the group's first top 40 entry on the Billboard Hot 100, and was also certified platinum in the United States.

The success of "Worth It" was largely impacted with televised performances on the season finale of Dancing with the Stars, and their debut late night appearance on Jimmy Kimmel Live on June 18, 2015, alongside Kid Ink for the first time.

[54] The album was supported by the group's first major headlining tour, the Reflection Tour, visiting 63 cities in North America and 6 cities in Europe[55] Fifth Harmony returned to the White House on April 6, 2015, to perform at the annually-held White House Easter Egg Roll, where they sang "Happy Birthday" as part of the Fifth anniversary of First Lady Michelle Obama's "Let's Move" initiative.

[56] Later that year, the group released "I'm in Love with a Monster" on September 25, 2015, a song for the film Hotel Transylvania 2 which was featured in the trailer and included in the movie as well.

[58] Critically, Reflection landed in several mid-year and year-end lists, including Rolling Stone and Complex who ranked the album at 39 and 9 in the exclusively pop category, respectively.

The lead single, "Work from Home", which features American singer Ty Dolla Sign was released on February 26, 2016, along with its music video.

The group won two MTV Video Music Awards for "Work from Home" and "All in My Head (Flex)" and was named by Billboard the "hottest young stars" under 21 for 2016.

[71] On July 24, during an appearance on The Tonight Show Starring Jimmy Fallon, the group announced that their third studio album would be titled Fifth Harmony.

[72] The girls performed on the 2017 MTV Video Music Awards, where they started with the promotional single "Angel", before transitioning to "Down" featuring Mane.

On October 26, they released "Por Favor", a duet with rapper Pitbull, as the third single from the Spotify re-release of the album and performed it at the 2017 Latin American Music Awards.

[82][83] The group began their PSA Tour on September 29 in Santiago, Chile, with Becky G serving as opening act in several Latin American countries, including Mexico and Argentina.

[102] Lana Del Rey, Adele, Janet Jackson, Celine Dion, Taylor Swift, Brandy, Jennifer Lopez, Patti LaBelle, Cher Lloyd, Carrie Underwood, Jessie J, Beyoncé, Alicia Keys, Christina Aguilera, Selena, Celia Cruz, Demi Lovato, Ed Sheeran and Leona Lewis have influenced individual members of the group.

In 2022, MTV credited Fifth Harmony for challenging several of the stereotypes associated with girl groups, pouring their voices into their music and speaking out against misogyny and abuse of power, stating that "Fifth Harmony were also inheriting the low retention rate of girl groups in American popular music, which has long been driven by the misogynistic belief that multiple women couldn't function on a collaborative level without falling out with one another in a fight for the spotlight.

Fifth Harmony was involved in a long-time confliction with their ex-label for alleged mistreatments[122] and the ownership of their music, in an interview with Billboard member Lauren expressed that "We'd put blood, sweat and tears — and birthdays and funerals we missed — into this thing, it's our livelihoods and our families, this is the train, and now you're like, 'Is the conductor going to come through with the coals, or are we left here to die?

"[118] In 2015, the group contacted a music lawyer that helped transfer the Fifth Harmony's trademark from Simon Cowell to its members, becoming the total owners of such.

[123] In 2016, journalist Hugh McIntyre of Forbes, declared "It's safe to say that Fifth Harmony doesn't have any real competition worth speaking of in the girl group lane".

[124] The Daily Trojan stated that "Fifth Harmony established themselves as the most popular girl group of the new generation — a void that desperately needed to be filled after the dissolution of the Pussycat Dolls and Danity Kane.

[126][127] Three members of Fifth Harmony (Camila Cabello, Normani, and Lauren Jauregui) have charted on the Billboard Hot 100 as soloists, which made them the fourth girl group to achieve this.

[129] Their biggest hit "Work from Home", became the highest-charting single in the United States and the first top-five entry from an all-female group to chart in ten years since "Buttons" by the Pussycat Dolls, which peaked at number 3.

In 2019, the song was placed fourth on the U.K. Official Charts Company's list of the "Top 100 girl band singles of the last 25 years", which was the highest position for an international or American act.

Sony Music Entertainment announced that they would be launching endorsement deals between Fifth Harmony and a number of companies, including two clothing lines with Wet Seal.

The first clothing line with Wet Seal was launched in August 2014 in 200 stores across America, featuring a collection from each member based on their individual style.