2013–present: Transition to lead roles
In 2013, Yeo starred as the titular character in action thriller Hwayi: A Monster Boy, for which he garnered praises and won several Best New Actor honors from annual award ceremonies such as Blue Dragon Film Awards and Korean Association of Film Critics Awards. He is the youngest male actor to receive the Best New Actor award in the history of Blue Dragon Film Awards, at the age of sixteen. In the same year, he was also cast in the sitcom, Potato Star 2013QR3 as an aspiring mobile application developer.
In 2015, he starred in the film Shoot Me in the Heart, based on the bestselling novel of the same name by Jeong Yu-jeong. He had his first leading role on television with teen vampire series, Orange Marmalade, based on the webtoon of the same name. He won Best New Actor Award at 2015 KBS Drama Awards for his role. In the same year, he appeared in the Korean War film, The Long Way Home. Veteran actor Sul Kyung-gu, his co-star in the film, strongly recommended Yeo for the role of Yeong-gwang, and only signed the movie contract once Yeo's casting had been finalized.
In 2016, Yeo played the role of King Yeongjo in the SBS drama The Royal Gambler, and won an Excellence Award at the year end SBS Drama Awards.
In 2017, Yeo starred in tvN's science fiction drama Circle, and historical movie Warriors of the Dawn, both of which premiered in May. He was also cast for a special appearance in the star-studded film, 1987: When the Day Comes, based on the June Democratic Uprising. The movie reunited him with Director Jang Joon-hwan and actor Kim Yoon-seok of Hwayi: A Monster Boy. In July, he starred in SBS's romance drama Reunited Worlds.
In 2018, Yeo was cast in the romantic comedy My Absolute Boyfriend, based on the Japanese manga series of the same name. It aired on SBS the following year.
In 2019, he starred in tvN's remake of the 2012 Korean film Masquerade, titled The Crowned Clown, playing dual roles as clown Ha-seon and King Yi Heon for which he received the nomination for the Best Actor - Television at 55th Baeksang Arts Awards. The same year, he was cast in Hong sisters' fantasy mystery drama Hotel del Luna alongside IU. The drama was a commercial success, recording the highest ratings in its timeslot throughout its run.
In 2020, Yeo made a special voice appearance in the drama Start Up as Jang Young Shil, the AI speaker. He also made a live action cameo in the final episode as a start-up owner named Hong Ji Seok.
In 2021, Yeo starred in the psychological thriller drama Beyond Evil directed by Shim Na-yeon alongside Shin Ha-kyun as the main leads which premiered in February and aired on JTBC. Shin Ha-kyun and Yeo previously appeared in the film No Mercy for the Rude (2006) where Yeo played the younger version of Shin's character. And in June 2021, Yeo was confirmed as an MC for Girls Planet 999 which aired on Mnet in August.
In 2022, Yeo starred in the tvN fantasy-melodrama Link: Eat, Love, Kill as a sous chef at a high-end restaurant. Later that year, Yeo made his return to the big screen after five years with Ditto, a remake of the 2000 film of the same name.
In May 2023, Yeo signed with J-Full Entertainment.
In 2024, Yeo portrayed a terrorist and plane hijacker in 2024 disaster film Hijack 1971, which marked his first villainous role in his 19-year career; the events of the film was based on a real-life plane hijacking incident in 1971 when the relationship between North Korea and South Korea became fraught with tensions. In an interview with Singapore's national newspaper The Straits Times, Yeo described it as a challenge to portray an antagonist for the first time in his career and he himself doubted whether he could play it well, but he credited his co-stars Ha Jung-woo and Sung Dong-il for helping him to immerse in the role.
