He fully committed himself to an acting career in 2017 where he starred in several movies as supporting roles, including in Kim Seong-hun's Confidential Assignment (2017), Lee Joon-ik's film Anarchist from Colony (2017), Ryoo Seung-wan's historical film The Battleship Island (2017), Min Kyu-dong's Her Story (2018), Lee Joon-ik's Sunset in My Hometown (2018), and Woo Min-ho's The Drug King (2018).

[2] Kim Jun-han was born on March 29, 1983, and raised in Changwon, South Gyeongsang Province,[a] where he lived until he graduated from high school.

Kim contemplated pursuing acting and held a modest belief that he would eventually make appearances in movies or dramas.

[18][19][20] In the film, Kim portrayed Datemas Kaisei, an examining Japanese judge who undergoes a transformation in his beliefs during the interrogation of the anarchist and revolutionary Park Yeol (Lee Je-hoon) and his lover Kaneko Fumiko (Choi Hee-seo).

[27][28] Kim's performances received praise from viewers, and his work in 2017 earned him a spot in the 2018 Cine21 Rising Star Actors feature.

[12] He reunited with director Lee Joon-ik and made a brief but impactful appearance in the film "Sunset in My Hometown" as Won-joon, a character who spoke in the Jeolla-do dialect.

[11] Kim underwent an acting transformation through antagonistic roles in two television series: MBC's Time (2018) and OCN's Quiz of God: Reboot (2018) respectively.

In his first lead role in MBC's Time, Kim played Shin Min-seok, the long-time lover of Seol Ji-hyeon (Seohyun).

After becoming a prosecutor, Shin Min-seok becomes a lawyer for W Group, where he oversees Cheon Soo-ho (Kim Jung-hyun), a troublemaking third-generation chaebol.

[30][31] In OCN's Quiz of God: Reboot (2018), Kim Jun-han portrays forensic expert Kwak Hyuk-min, known for his calm demeanor and commanding presence.

In the series, he portrayed Kwon Ki-seok, a successful bank audit department manager who seemed to have a perfect life due to his privileged upbringing.

As the story progressed, his obsession with Lee Jeong-in grew, causing conflicts with Yoo Ji-ho (Jung Hae-in), her new love interest.

[36] It aired from May 22 to July 11, 2019, and Kim's acting received positive recognition from viewers who felt a mix of sympathy and dislike towards his character.

Kim Jun-han takes on the role of Ahn Chi-hong, a resident in the neurosurgery department who carries unreciprocated affection for his professor, Doctor Chae Song-hwa (Jeon Mi-do).

[41][42] In subsequent year, Kim reunited with Jung Woo-sung in his directorial debut film A Man of Reason, with principal photography starting on February 10, 2020.

[48] In the end of summer of the same year, Kim participated in the Coupang Play original web series Anna, written and directed by Lee Joo-young.

Choi Ji-hoon is an ambitious and driven individual, and the CEO of a promising venture company that he established at a young age.

[57] Subsequently, on October 31, 2022, Kim signed with Artist Company, an agency founded by Jung Woo-sung and Lee Jung-jae.

[58] Kim led an acting study group that he founded with fellow actors, including Choi Hee-seo, Bae Ki-gi, and Yoon Seul, who had previously worked together in Anarchist from Colony.

[4] Director Lee Joo-young of Anna affectionately refers to Kim "Yeonba," which means a fool who only cares about acting.