It was released as a promotional single via S-Curve Records on March 12, 2019, for the band's third studio album Neotheater.

[1] Following the release of lead single "100 Bad Days", AJR announced the album's name and cover art on March 10, 2019.

[2] The album's tracklist was revealed in conjunction with the single release of "Birthday Party" on March 12, 2019.

[4] On the show BUILD Series, Jack Met tells that "Ryan and I are at Columbia and we're studying film, and in one of our classes we saw this movie called Eraserhead [...] and then we saw this one part where this guy goes in a radiator, and then this woman starts singing to him, and as soon as she starts singing this song we looked at each other, we stopped laughing, and we were like 'Oh my god, we have to use this on the album'".

[6] "Birthday Party" is composed in 44 common time and in the key of C-sharp major, with a tempo of 84 beats per minute (bpm).