Humes started his music career in a band called VS which was created by Blue member Simon Webbe; however shortly after being formed and releasing an album, they split. Humes appeared in Holby City on the BBC for three years from 2000 to 2003 playing Robbie Waring for 14 episodes. At the age of 14, he starred in a children's programme called K-Club, which helped people with computers and how they work.
Oritsé Williams decided to get into the music business mainly. He was originally scouted for a number of boy bands but did not feel they were right, Williams decided to form his own boy band and, through friends, met Marvin Humes who had experience in R&B and pop music, being a part of VS in 2004. Next to join was Aston Merrygold, who was once cast in the ITV children's programme Fun Song Factory, because of his athletic ability. Last to join the group was JB Gill, for his "musical ear" and harmonies. They bonded, became friends and together they were called UFO (an initialism of Unique Famous Outrageous). They signed to Tracklacers developing a sound they then called "Jack the Lad Swing", combining the phrase "Jack the lad" and the urban music of new jack swing. While working their way into the music business, UFO instantly signed to Epic Records, before winning their first award in late 2007 at the Urban Music Awards for Best Unsigned Act thanks to their mash-up of "Stand by Me" by Ben E. King and "Beautiful Girls" by Sean Kingston. Shortly thereafter, they released their second single, "Slap Ya Elbow". The group give credit to "DJ Triz" who produced one of UFO's first songs and helped them write it.
In 2008, UFO auditioned for the fifth series of The X Factor, but had to change their name because it was already being used by another group, so they decided to go with the name JLS (an initialism of Jack the Lad Swing, the style created with Tracklacers some months back). Following the elimination of girl groups Bad Lashes and Girlband in weeks one and two respectively, JLS were Louis Walsh's last remaining act in the competition, but throughout the live shows the judges called them the best band to come out of The X Factor. In week 7, JLS were in the bottom two along with Rachel Hylton. However, they survived, thanks to votes from Walsh, Cheryl Cole and Simon Cowell. Cowell stated when casting his deciding vote that JLS did not deserve to be in the bottom two. In week 8, JLS performed "...Baby One More Time" and received negative comments from two of the four judges, with Cowell saying "at the moment you're out", but after their second performance, "You Light Up My Life", Cowell commented that they were "back in the race" and that they could "have a hit record" with the performance.