Prior to the final of Phantom Singer 2, Kang was grouped together with Bae Doo-hoon, Cho Min-kyu and Ko Woo-rim to form Forestella. He had never been grouped with any of the other members up until the random quartet stage. They eventually won the competition and debuted on March 14, 2018.
Kang signed as a solo artist with Arts & Artists, which had also managed Forestella as a group until June 2021. In October 2020, he made his debut release with the digital single "Universe" under the stage name PITTA. It was the name of the band had been part of from his amateur days and he chose to use it as a homage to his members. In November 2021, he released the self-composed extended play ID: PITTA, his first non-single release as a solo artist.
He participated in various televised music competitions, like King of Mask Singer, where he was eliminated in the first round, but showcased a wide vocal range. He finished 5th overall in the celebrity singing competition Lotto Singer, despite receiving the highest score from judges.