Her directorial film debut Past Lives (2023) received critical acclaim, and was nominated for the Academy Award for Best Picture and Best Original Screenplay.

[10][2] In a mixed review, Alexandra Schwartz of The New Yorker described Endlings as "two works spliced roughly together: a traditional play that seeks to depict people’s lives, and a metafictional examination of the playwright’s own motivations, which flirts with honesty before traipsing down a solipsistic path of no return.

[13][2] In a review for Vulture, Helen Shaw praised the experimental play: "I think Song’s game-play/play-game managed the trick by capturing the experience not of going to a show but of working on one.

"[14] Song's other plays include Tom and Eliza, which was named a semifinalist for the American Playwriting Foundation's 2016 Relentless Award, Family, and The Feast.

"[12] Song wrote the screenplay for Past Lives, her directorial film debut, about two childhood friends who later reunite as adults (portrayed by Greta Lee and Teo Yoo).

[18][19] The Guardian's Benjamin Lee wrote that "as writer, Song manages to keep her dialogue believably light-footed and spare while as director, she confidently and evocatively captures both cities with a breadth that belies her inexperience".

[20] Richard Lawson of Vanity Fair hailed the film as "understated and yet vast in its consideration of the slow changes of life, of the past ever whispering to the present.