Lee made his acting debut in the film Cold Eyes (2013), and since then he has starred in notable television series such as Good Manager (2017), Rain or Shine (2017–2018), King the Land (2023).

[2] Lee participated in an undergraduate programme at Howon University located in Gunsan, South Korea, with his bandmates Chansung and Wooyoung.

[5] In 2008, he participated in Mnet's show Hot Blood Men[6] a program that chronicles the rigorous training of thirteen aspiring trainees, all vying for a coveted spot in the boy band One Day.

However, their second EP, 2:00PM Time For Change, propelled their triumph within the realm of Korean music, solidifying their meteoric rise.

[21] On December 3 and 4, Lee orchestrated a special encore concert titled "Last Hyper Night" at Nippon Budokan.

[23] This particular album marked a significant achievement for Junho, attaining the impressive rank of number two on Oricon's weekly music chart.

1 position on the daily album chart maintained by Japan's foremost music statistics-tracking entity, Oricon, boasting an estimated sale of 27,270 units.

[29] His summer solo tour "Flashlight" commenced in late June and extended until early September, featuring thirteen performances across five cities in Japan.

[30] On December 5 the same year, Lee introduced a Japanese compilation album titled Junho the Best featuring a collection of sixteen tracks.

[35] After filming King the Land (drama), Lee immediately launched into an Arena Tour full concert in Japan, called "the Day We Meet Again" (Mata Aeru Hi).

[50] In 2018, Lee was cast in his first Japanese movie Rose and Tulip, written by popular manga artist Akiko Higashimura, in which he played a double role.

[55] In November 2021, he starred the historical romance drama The Red Sleeve, playing the role of Crown Prince Yi San, alongside Lee Se-young as Royal Consort Uibin Seong.

In 2012, Lee collaborated with actress Kim So-eun on MBC's program Music and Lyrics for the creation of the song "Sad Love".

Crafted by Kim So-Eun and composed by Junho, this single garnered significant acclaim, promptly securing positions within the top 10 ranks of diverse music charts.

[63] The composition "Move On," a collaborative work between Lee and fellow member Jang Wooyoung, emerged with 2PM's compilation album 2PM Best~ 2008–2011 in Korea, subsequently surging to the zenith of Japan's Recochoku Chart.

[64] In 2013, Lee ventured into composing for Wooyoung's Korean debut EP, 23, Male, Single contributing to the track "Be With You".

[65] "Love Is True," a melodious creation graced by the vocals of Lee and Nichkhun, found its place in the supplementary CD of 2PM's Korean album Go Crazy!

Another notable musical accomplishment came in the form of "Versus," a collaborative effort by Lee and Hwang Chan-sung, which he penned and recorded for the limited edition version D of 2PM's Japanese album, Galaxy of 2PM.

Due to a severe shoulder injury he suffered in 2010 during an acrobatics practice and for which he underwent major surgery in 2012, he was judged unfit for active duty.