Song Jae-rim began his career as a model before transitioning as an actor in 2009 with a minor role in the movie Actresses. In 2012, he became part of the hit MBC sageuk The Moon That Embraces the Sun. In 2014, he was paired with Kim So-eun in the fourth season of the MBC reality-variety show We Got Married, which won him the Best Male Newcomer honors at the MBC Entertainment Awards. He and Kim So-eun also bagged the Best Couple Award at the ceremony. In 2015, he acted a supporting role in the KBS2 series Unkind Women, which earned him a Best New Actor nomination at the KBS Drama Awards. In 2016, he reunited with Kim So-eun in the SBS romantic comedy Our Gap-soon, which scored him a Special Acting Award at the SBS Drama Awards. In 2018, he was nominated for a Top Excellence Award at the SBS Drama Awards for his work in the mystery thriller Secret Mother.

Song Jae-rim studied electrical and electronics engineering at the Chung-Ang University. He can play the saxophone well. He started playing the instrument to strengthen his lungs after a surgery.