Sohn Seok-gu began his acting career in 2014 with a small role in the film Scarlet Innocence. In 2017, he had an appearance in the Netflix sci-fi drama Sense8. In 2018, he landed roles in the KBS2 dramas Suits and Matrimonial Chaos, which earned him a Best New Actor nomination at the KBS Drama Awards. His work in the latter also scored him a nomination for Best New Actor for TV at the 55th Baeksang Arts Awards. Additionally, he was nominated for Best New Actor for Film at the 55th Baeksang Arts Awards for his performance in the 2019 movie Hit-and-Run Squad. Also in 2019, he became part of the tvN drama Designated Survivor: 60 Days, which was based on the American TV series Designated Survivor. The drama bagged the Best Adaptation of an Existing Format citation at the 2019 Asian Academy Creative Awards.

Sohn Seok-gu went to Iraq as part of the Republic of Korea Army’s Zaytun Division for his mandatory military service. The said division carried out peacekeeping and reconstruction-related tasks in Iraq during the Iraq War. He learned to speak English fluently after living and studying in the United States and Canada.