Siwon was scouted by SM Entertainment when he was 16 years old and then went on to audition for the company’s Starlight Casting System. Siwon’s parents were notified only after he passed the auditions. Siwon has already appeared in a music video and two TV dramas before he debuted with the 12-member South Korean boy band Super Junior 05 on November 6, 2005. The group later dropped the suffix “05” from its name following the addition of its thirteenth member Kyuhyun. In 2008, Siwon became a part of the Super Junior-M, which is Super Junior’s Mandapop subgroup for the Chinese music industry.

Siwon made his movie debut in the 2006 Hong Kong epic film A Battle of Wits. In 2010, he joined the cast of the SBS romantic comedy series Oh! My Lady, in which he earned the New Star Award at the 2010 SBS Drama Awards. In 2015, Siwon starred in multiple projects in and out of South Korea, including the Hong Kong historical action movie Dragon Blade together with Jackie Chan and the MBC workplace romantic comedy She Was Pretty. Siwon received an Excellence Award nomination at the 2015 MBC Drama Awards for his work in the series. In 2019, he took home an Excellence Award at the KBS Drama Awards for the crime comedy My Fellow Citizens.

Siwon came from an affluent family. His father was the former CEO of the pharmaceutical company Boryung Medicine. He enlisted for his mandatory military service on November 19, 2015 and was discharged on August 18, 2017. He is also active in philanthropy. Since 2010, he has been part of several UNICEF campaigns. In 2015, he was appointed as UNICEF Korea Special Representative. In 2017, he was caught in a controversy after an untied French bulldog owned by his family bit a neighbor, which resulted in the victim’s death.