In 2010, Seungyoon was a contestant on Mnet's singing contest Superstar K2.
He finished the show in fourth place, while having released two singles, "I'll Write You a Letter" and "Instinctively". "
I'll Write You a Letter" peaked at number 24 on the Gaon Music Chart after its release on the Superstar K2: Top 6 (My Story) album, while "Instinctively" became a number-one hit single in South Korea, selling almost 2 million digital copies and was listed as one of the top 100 songs in the year-end charts.
It was released on its own as a digital single later in the Superstar K2 compilation album, Superstar K2 Up to 11.
The single went on to earning him the "Rookie of the Year" award at the Gaon Chart Awards in addition to the "Rookie of the Month (October)" at the Cyworld Digital Music Awards.
He also released the promotional single, "Life is Tab" alongside three other contestants to promote the Samsung Galaxy Tab.
On November 28, Seungyoon performed at the Mnet Asian Music Awards held in Macau, China alongside other Superstar K2 contestants.

After initial success with Superstar K2, Yang Hyun-suk signed Seungyoon to YG Entertainment as a trainee on January 12, 2011.
When asked the reasons for his decision to sign with the company, he answered: "Since Superstar K2 ended, there were a lot of offers.
Some said they would make me the star of Asia, and some offered a great amount of money for signing the contract.
I chose YG Entertainment because this agency evaluated me objectively, unlike other ones.
They looked at me as an actual trainee."
He also released a single, "You Are Heaven", for the soundtrack of the Korean drama Midas.
Seungyoon graduated from Busan High School of Arts with a major in classic guitar in 2012.
That same year, he appeared on MBC's sitcom High Kick: Revenge of the Short Legged.
He plays as a young man with a heavy southern-Korean accent who arrives in Seoul dreaming to become the President.
The series aired from September 19, 2011 to March 29, 2012.
In 2010, Seungyoon was a contestant on Mnet's singing contest Superstar K2. He finished the show in fourth place, while having released two singles, "I'll Write You a Letter" and "Instinctively". "I'll Write You a Letter" peaked at number 24 on the Gaon Music Chart after its release on the Superstar K2: Top 6 (My Story) album, while "Instinctively" became a number-one hit single in South Korea, selling almost 2 million digital copies and was listed as one of the top 100 songs in the year-end charts. It was released on its own as a digital single later in the Superstar K2 compilation album, Superstar K2 Up to 11. The single went on to earning him the "Rookie of the Year" award at the Gaon Chart Awards in addition to the "Rookie of the Month (October)" at the Cyworld Digital Music Awards. He also released the promotional single, "Life is Tab" alongside three other contestants to promote the Samsung Galaxy Tab. On November 28, Seungyoon performed at the Mnet Asian Music Awards held in Macau, China alongside other Superstar K2 contestants.
After initial success with Superstar K2, Yang Hyun-suk signed Seungyoon to YG Entertainment as a trainee on January 12, 2011. When asked the reasons for his decision to sign with the company, he answered: "Since Superstar K2 ended, there were a lot of offers. Some said they would make me the star of Asia, and some offered a great amount of money for signing the contract. I chose YG Entertainment because this agency evaluated me objectively, unlike other ones. They looked at me as an actual trainee." He also released a single, "You Are Heaven", for the soundtrack of the Korean drama Midas. Seungyoon graduated from Busan High School of Arts with a major in classic guitar in 2012. That same year, he appeared on MBC's sitcom High Kick: Revenge of the Short Legged. He plays as a young man with a heavy southern-Korean accent who arrives in Seoul dreaming to become the President. The series aired from September 19, 2011 to March 29, 2012.
Kang Seung-yoon