In 2013, at the age of eighteen, Lee Tae-hwan made his official acting debut in the short TV series titled After School: Lucky or Not together with the members of 5urprise. He next starred in High School King of Savvy, portraying a ice hockey player.
In 2014, Lee starred in MBC drama Pride and Prejudice, where he played an investigator and former taekwondo athlete. Lee's then starred in his first period drama, Splendid Politics in which he played young Prince Gwanghae.
From 2016 to 2017, Lee was cast in MBC's weekend drama Father, I'll Take Care of You, a 50-episode family drama in which he portrayed one of the unmarried sons. He then starred in another weekend drama My Golden Life from 2017 to 2018, playing an industrial design student. The drama was a hit with over 40% ratings, and led to a rise in popularity for Lee.
In 2018, Lee was cast in tvN's romantic comedy drama Why Secretary Kim, playing a famous author.