While many of the members took part in various activities before the group's formal debut, according to their agency, all of them had been training together for two years and the average training time among the members was 4 years. Chinese member Cao Lu was previously a solo singer in Mainland China after winning a 2004 CCTV sponsored singing contest. Her album, titled Cat, was released in 2005 under her former stage name, LuLu

Maknae and main rapper Yezi also became famous as an underground rapper even before she debuted, since she released various rap mixtapes on her account and garnered high praises from netizens before she was planned to become a member of the group.

Leader Jei did modeling for various online clothing stores and was the female lead for boy band Infinite's music video for their song 'Paradise', Bongshil Sister's My Love and also for Taw's music video for Happy Hours featuring Joo and the Lifestyle. She later replaced Joo on the promotions due her being diagnosed with a bump on her throat, and became fine right after the promotions ended.

Linzy was a trainee under YG Entertainment and was originally planned to be a 2NE1 member and is also one of the trainees to be originally planned to become a member from YG's new girl group (with the idea scrapped in 2012, and the group disbanded even before debuting) and recorded a song for the 2010 Korean drama Obstetrics and Gynecology.

Leader Jei appeared on Infinite's Paradise music video and also featured in Taw's Happy Hours music video with the featuring of Joo with the Lifestyle. Hyemi and Jei both starred in IU's Good Day and You & I music video as backup dancers, the whole group starred in Sunny Hill's Midnight Circus music video as backup dancers.

Only USA-born member Cheska don't have any past connections on the entertainment industry.

LOEN Entertainment initially announced that they would be debuting a six member girl group that contained not only members from South Korea, but from China and the United States as well. After revealing the names and pictures of the members, it was revealed that they would be singing a duet with label mate IU prior to their debut for their agency's artist collaboration album. Titled 'Sea of Moonlight', the song ranked high on the Korean music charts.

In August, the group's debut single "Vista" was announced and it was revealed that they would also be collaborating with hip-hop artist Tiger JK for a pre-release song called "Wicked", which received much attention for its Reggaeton influence. JYJ's Junsu made a guest appearance in the music video for "Vista" along with Seungah from Sunny Hill. Their song Vista charted high on charts, with the other songs all charting on the Billboard Hot 100.

On November 1, member Cheska revealed the girls were planning to comeback, which was later confirmed by LOEN following the release of the teaser image, along with the comeback date of November 9, 2012 with their second single album, We Don't Stop. We Don't Stop is revealed to be with the works of Hyuk Shin. The B-side for single, Sweet Love, was released on November 5 and featured ballad singer Kim Yeon-woo. The promotions followed on Music Bank on November 10, 2012.

Members had some individual activities, like Jei appearing in TVN's love-reality show, Romantic and Idol, alongside AOA's Hyejeong, 4Minute's Jihyun, and more. Members Jei, Cheska, and Yezi appeared alongside IU for comedy show, Gag Concert. Linzy and Hyemi appeared in KBS's singing show, 1000 Songs Challenge. The whole group also appeared in Weekly Idol, and on Dream Team 2. The group also made an endorsement with HIM Magazine.

Fiestar's begun the 2013 by ending their promotions of We Don't Stop on Simply K-pop, and also appearing KBS' 1 vs. 100. Cao Lu also appeared on Dream Team 2. They appeared on shows again last May 2013, appearing on various shows, with the whole group appearing on SBS' Ggurugi Life Inquiry, KBS' Family Love, MBC Music's All the K-pop with only Cao Lu and the show Stress Out along with Spica. Member and leader Jei also appeared on their brother group History, appearing in all individual teasers of each 5 members, with the theme "Romantic Dating Tips".

Member Linzy joined the cast of the Korean musical rendition of the 2006-2008 musical movie hit High School Musical taking the role of Sharpay Evans, sharing the role with The Grace's Dana. The musical also shows a tremendous cast with Super Junior's Ryeowook, F.T. Island's Jaejin, f(x)'s Luna, AOA's Choa and musical actress Oh So-yeon. The photoshoot begun at June 28, and begun the show at July 2, at Blue Square Samsung Card Hall.

Last July 25, LOEN released a picture with Jei, Cheska, and Cao Lu holding up a book while looking at the camera, and released a statement that Fiestar will be creating an educational program entitled, "Fiestar's A-HA! For the Global K-Pop Fan", for international viewers who wants to learn the Korean Language. The first video is released on July 26, with their main topic, "Daebak", with Jei speaking Korean, Cheska in English, and Cao Lu translating it in Chinese.

Fiestar made a CF for the Samsung's Zoom Camera Feature for Samsung Galaxy S4, with the full commercial released on June 30. Member and leader Jei had a pictorial with SURE Magazine, hinting of a comeback somewhere beginning on the second half of 2013, and another album with the help of Eric Benét. Member Cheska also updated their fancafe, hinting of a comeback drawing near. Their comeback is announced on August 22 with a digital single, and is said to be with the works of Eric Benet. The digital single is titled "Whoo!", with a sneak peek 10-second audio clip released at the end of the group's 'A-HA' 5th lesson video. LOEN Entertainment announced that Whoo! will just be a pre-release single for their upcoming comeback. The whole song collaboration with Eric Benet is released on August 27, and featured a Latin R&B music, introducing a new sound from Fiestar. The song ranked high on music charts, despite no live promotions.

In September LOEN announced a multi-label system and FIESTAR changed labels from LOEN Entertainment to Collabodadi.

• 4th Annual Seoul Success Awards "Best Rookie of the Year"
  
• 2012 Arirang's Simply K-Pop Awards "Super Rookie Idol of the Year"
  
• All the Kpop - World-Class Rookie Awards "Rookie of the Year" & "Knock-Out Award"
  

• 2012 AllKPop Awards "Best Live" & "Best Female Rookie"
  
• 22nd Seoul Music Awards "Rookie Award" & "Popularity Award"
  
• 2012 EYK Awards "Best Aegyo"
  
• 2012 KU Awards "Best Female Rookie"