Yoo Youngjae was born in Uijeongbu, South Korea, on January 24, 1994. Youngjae has one older brother. He studied at the Balgok elementary school and Balgok middle school. In 2008, Youngjae placed first in a JYP audition and was a JYP trainee. Yoo contacted TS Entertainment and got accepted as a trainee after his audition. When asked how he became a singer, Youngjae commented, "At a field trip, there was a talent show. At that time I sang on stage, my friends cheered loudly and it was surprising. That was the start. My dream to stand on stage is the career I want so I thought “I’ll become a singer.” I dreamt of becoming a singer, and started to study music, rapidly becoming attached to the attraction of music. I love music, concentrating on that passion, I became a B.A.P member, and that’s that. I prepared at another company for a year, but when I saw that I couldn’t debut, I was contacted by this company and debuted about a year later. My life as a trainee wasn’t especially hard. Instead, in order to become a pro, I had to prepare my true abilities and individuality and I thought “This is my responsibility I have to carry” and feel pressure because of this." In 2011, he also appeared in the music video of Secret’s "Starlight Moonlight" and performed with Secret during the promotional period. And also appeared in the music video of Bang&Zelo’s "Never Give Up".
In March 2011, TS Entertainment already signaled that they will debut a boy band in 2012. Bang Yong Guk was the first member to be revealed in TS Entertainment's upcoming boy band with singles such as "Going Crazy" and "I Remember". In August 2011, TS Entertainment introduced its second member, Kim Him Chan and revealed that he will be an emcee in MTV's The Show. In November 2011, TS Entertainment stated that they will debut a sub-unit group for their upcoming boy band previously known as "TS Baby" featuring Bang Yong Guk and another member.
On January 18, 2012, TS Entertainment released the jacket photos for Youngjae and Himchan.B.A.P debuted in January 2012 with their lead single "Warrior". On January 28, 2012, the group held its debut showcase concert in Seoul, South Korea with over 3,000 people attended the show. Their debut single met them critical acclaim as various media outlets dubbed the song and its music video, "powerful and charismatic".