Lee Chanhyuk and Lee Suhyun lived with their parents in Mongolia for almost two years before they returned to South Korea to pursue a career in the music industry. The siblings, under the name Akdong Musician, became part of the Proteurment agency. Under the company, they did several stage performances and even released an original song called "Galaxy", which was later used as a soundtrack for a Samsung Galaxy S4 commercial.
In August 2012, the duo participated in the preliminary auditions of K-pop Star 2, which were held at Jamsil Arena in Seoul. They passed their audition, and in the show's first round they sang a cover of Miss A's "Breathe" and an original song titled "Don't Cross Your Legs", to praise from all three judges. Park Jin-young, founder and CEO of JYP Entertainment, praised the chemistry between the siblings and the techniques they had incorporated in their performances. Singer and representative of SM EntertainmentBoA highlighted and praised the lyrics of their original song, while Yang Hyun-suk, founder and CEO of YG Entertainment, described them as "true artists" among the people who had auditioned for the show. The duo continued to receive positive responses from the judges, until after their second performance in the third round. The judges pointed out that their lack of confidence was the main reason behind their lukewarm performances in the succeeding rounds. In spite of this, they eventually won the competition.
Some of their original songs performed during the competition were released under LOEN Entertainment and were well received; "You are Attractive", released on 12 December, immediately reached the number one spot on the Gaon Charts. After the competition, despite not being signed under an entertainment agency, they participated in commercials and composed several songs. One of these songs was "I Love You" for the television seriesAll About My Romance.
On 24 May 2013, a month after winning K-pop Star 2, the siblings signed an exclusive contract with YG Entertainment.
Akdong Musician's debut album, Play, was released digitally on 7 April, and physically on 9 April, nine months after winning K-pop Star 2. The album has eleven songs, all written and produced by Lee Chanhyuk. It has a total of three title tracks accompanied by three different music videos, with the third title song determined by fan voting. The first song, "200%", was chosen by Yang Hyun-suk, and the second song, "Melted", was chosen by Akdong Musician. The album debuted at number two on Billboard's U.S. World Albums Chart. Akdong Musician's debut stage was on K-pop Star 3 on 6 April.
The music video for "200%" was released on 7 April along with the digital album. Shortly after its release, "200%", topped the music charts, with the rest of the songs on the album also charting high. The music video for "Melted" was released on 14 April. The last and third title song was "Give Love", which was the third high-charting song, after "200%" and "Melted". The music video for "Give Love" was released on 2 May.
On 16 June, Akdong Musician participated in YG Family's cover project, releasing a cover of Taeyang's "Eyes, Nose, Lips".
Akdong Musician's first live concert tour, called "AKMU Camp", took place on 21–23 November at Blue Square Samsung Card Hall, Hannam-dong, Seoul.
On 10 October, Akdong Musician released a digital single, "Time and Fallen Leaves" (Hangul: 시간과 낙엽; RR: Sigan-gwa Nagyeop), written and composed by Lee Chanhyuk. It was originally going to be the title track of Play, but was held back for an October release because it suited the autumn season better. The song made an "all-kill" two consecutive days after release by ranking number 1 on nine major real-time music charts. It also ranked number 1 on the weekly Gaon Digital Chart the second week of release. The song was not given a music video so the listeners would imagine their own stories.