2011–2017: Theater and breakthrough roles in television
In 2011, Park had the opportunity to act on stage even though he had little acting experience. During his performance in his first theater play, Inside the Minke Whale, the joy of acting that he had forgotten about was rekindled. The following year, he also took on minor roles in two television dramas, which as soldier in MBC historical drama Moon Embracing the Sun and as high school student KBS2 drama Big. Shortly after, Park joined the fifth season of the popular play Cats on the Roof, for which over 1,000 actors applied. Despite the fierce competition ratio of 150 to 1, Park was selected for the titular role of Lee Kyung-min. He reprised this role in the sixth season as well.
In the first six months of 2013, Park had a busy schedule. Park played the role of Lockwood in Korean premiere of Alan Bennett's play The History Boys. Subsequently, He had the task of balancing his obligations in both the MBC drama You Are the Boss! and the play Model Students. In drama You Are the Boss! he appeared as Yu Deok-hwa, the high school classmate of the main character Lee Seon-nam (played by Shim Hyung-tak). Simultaneously, he met the audience in the role of Seo Min-yeong, a model student with a shrewd paranoia, in the play Model Students. Juggling two different projects simultaneously and switching between such contrasting characters was undoubtedly challenging. Park stated that he enjoyed the process.
Following a short break, his next project was a guest appearance in John Cariani's omnibus play Almost, Maine. This performance was a special stage commemorating the 10th anniversary of the theater company Ganda. Producer Ahn Hyeok-won invited him and Park's decision to participate as a guest was influenced by his agency mates, Jin Seon-kyu and Lee Hee-joon, who were members of Ganda. In the fifth episode titled "They Fell", Park appeared as Chad opposite Yoon Na-moo as Randy, with whom he had previously worked in the play Model Students.
In 2014, Park appeared as a communications team leader in SBS drama Three Days and worked alongside senior actors in the industry. Then Park joined performance delivery service Ganda's play Judo Boy, as Min-wook, a boxer. This was one of his memorable performances was a result of developing camaraderie with his fellow actors, as they practiced together for four to five months.
In the end of that same year, Park and Jo Kang-hyeon both portrayed the character Park Jae-hyun in the play Melodrama directed by Jang Yu-jeon. Park Jae-hyun, who underwent a heart transplant after a car accident in his youth, falls deeply in love with Seo-kyung. Melodrama premiered in 2007 and received positive reviews for its artistic value and exploration of adultery, conveying a message about the true essence of love. It was performed at the Jayu Theater in Seoul Arts Center from December 31, 2014, to February 15, 2015.
In 2015, Park reprised his role in Judo Boy. He also returned to the play Model Students after a two-year break. In 2013, he had previously portrayed the role of Min-yeong. In 2015, Park, along with Kang Ki-dung, was double cast as the character of Myeong-jun, who had a false sense of inferiority hidden beneath his composed demeanor.
In autumn, Park and Jeong Dong-hwa were both cast as Oliver in a revival of the play The Pride directed by Kim Dong-yeon. The central theme of the play focused on the social struggles faced by marginalized groups, particularly sexual minorities: Philip, Oliver, Peter, and Sylvia, who lived in two different time periods—1958 and the present day. The production took place at the Daehakro Soohyun Theatre and ran from August 6 onwards. The Pride is a play by Alexi Kaye Campbell, a Greek-British playwright. It originally premiered at the Royal Court Theatre Upstairs in November 2008 and received prestigious awards such as The Critics' Circle Prize for Most Promising Playwright and the John Whiting Award for Best New Play. The production, under the direction of Jamie Lloyd, also received a Laurence Olivier Award for Outstanding Achievement in an affiliate theatre. The South Korean adaptation of the play was written by Ji Yi-seon, translated by Kim Soo-bin, and made its debut at The 5th Best Plays Festival at the Art One Theater in 2014.
In October of that same year, in historical drama Six Flying Dragons, Park played Gil-yu, the son of Gil Tae-mi (Park Hyuk-kwon) and a delinquent Confucian student in Sungkyunkwan. He won Best New Actor Award from Korean Culture Entertainment Awards for the role.
In the end of the year, Park joined Koki Mitani's play University of Laughs directed by Taeyoung Jeong, featuring actors Seo Hyun-cheol, Nam Seong-jin, Park Seong-hoon, and Lee Si-hoon. In the press call, Park mentioned that compared to his previous play, this play was even more challenging as it was a two-hander performance. Park expressed that after working on heavy projects consecutively, he wanted to do a comedy, and University of Laughs provided him with that opportunity. He also mentioned that memorizing the repeated and similar but different lines in the performance was the most difficult part. It was staged at Daehakro Arts Plaza Hall 1 until January 24 of the following year.
Park appeared in several productions, including the popular play The History Boys, Model Students, Judo Boys, and Melodrama. He also fearlessly embraced roles pertaining to homosexuality in productions like The Pride and Two Weddings and a Funeral. His dedication to immersing himself in any role he took on earned him acclaim as an actor. As a result, he earned the nickname "theater idol" and developed a following among theater audiences. However, despite his popularity within the Daehangno theater community, he had yet to attain widespread recognition from the general public.
In 2016, Park made a comeback to the play Almost, Maine at the Sangmyung Art Hall in Jongno District, Seoul, after three years. The performance took place from January 8 to April 10. In this performance, appeared in three different roles in three episodes, including "Where It Went," which depicts realistic love between two men and women. He said, "I met Director Min Joon-ho of the theater group Ganda and realized that I had been trying to act too easily. As Director Min is also an actor by profession, I received a lot of help in terms of 'eye-level explanations.'"
In July that same year, Park signed an exclusive contract with BH Entertainment. In the end 2016, he became scene stealer with his role as Secretary Cha in SBS drama Don't Dare to Dream.
In 2017, Park reprised his role as Oliver in the play The Pride directed by Kim Dong-yeon. The performance ran from March 21 to July 2, 2017, at the Daehakro Art One Theater Hall 2. Additionally, Park took on the role of reporter Na Sung-shik from the Splash Team in the drama Distorted. He also made a special appearance in Mad Dog as the insurance fraudster Go Jin-cheol. Furthermore, Park portrayed the supporting role of Park Gon in Black Knight: The Man Who Guards Me.
