Park Hae-jin made his acting debut in the 2006 KBS2 weekend drama Famous Chil Princesses, which won him Best New Actor at the 43rd Baeksang Arts Awards and the KBS Drama Awards. In 2007, he starred in the hit KBS1 daily drama Heaven and Earth, which earned him an Excellence Award at the KBS Drama Awards. In 2008, he took home the Best New Actor trophy at the MBC Drama Awards for his work in East of Eden. In 2012, he became part of the top-rating KBS2 family drama My Daughter Seo-young, in which he was nominated for Best Supporting Actor at the KBS Drama Awards. In 2013, he acted alongside Jeon Ji-hyun and Kim Soo-hyun in the widely popular SBS fantasy romantic comedy You From Another Star. In 2016, he was paired with Kim Go-eun in the tvN series Cheese in the Trap, in which he was named Best Actor at that year’s Korean Cable TV Awards. In 2020, he bagged the Daesang at the MBC Drama Awards for his performance in the comedy drama Old School Intern.

Park Hae-jin was exempted from mandatory military service in 2004 due to a mental illness. He has a large collection of sneakers.