Junho signed a contract with JYP Entertainment after he won the SBS reality show Superstar Survival in 2006. He debuted with the South Korean boy band 2PM in 2008 with the song 10 Out of 10. The following year, the group’s second single album titled 2:00PM Time for Change spawned the top-charting track Again and Again. Both songs were included in their first studio album titled 01:59PM. In 2013, Junho made his solo debut in Japan with the self-composed mini album Kimi no Koe. In 2017, he officially debuted as a solo artist in Korea with the mini album Canvas.

Junho made his big screen debut in the 2013 movie Cold Eyes, in which he scored a Best New Actor nomination at the 22nd Buil Film Awards. In 2017, he became part of the main cast of the KBS2 workplace drama Chief Kim. He won an Excellence Award at the 31st KBS Drama Awards for his work in the series. He then landed his first leading role in the 2017 JTBC romantic melodrama Just Between Lovers. In 2018, he headlined the SBS drama Greasy Melo along with Jang Hyuk and Jung Ryeo-won. In 2021, he acted alongside Lee Se-young in the hit MBC sageuk The Red Sleeve Cuff. His performance in the series earned him numerous acting citations including Best Actor at the 58th Baeksang Arts Awards.

Junho enlisted as a public service worker for his mandatory military service on May 30, 2019. He was discharged on March 20, 2021.