“Caleb originally wrote this song in a drunken state at during the very beginning of the recording sessions for their previous album Only By The Night but it never made the cut. He explained to The Music Fix how it ended up on Come Around Sundown: "We were going through the song titles and everything that we had and Angelo was like, ‘why don’t we try to record "Mary” again?’ And I could see everyone kind of go like ‘ehhh,’ but I was like, ‘Please!’ ‘Mary’ is something that I’ve always loved and I think that it would have been a travesty if it didn’t make this record."

Bassist Jared told The Music Fix how it originally sounded: “On the demo, it was really kind of distorted-sounding and it really had a Neutral Milk Hotel or a Olivia Tremor Control vibe. It sounds like… There’s a song called ‘Holland 1945’ by Neutral Milk Hotel that it really kind of… It’s this kind of bar song that’s like really fast. And I mean, when we recorded it, we kind of took it more of a Phil Spector way as opposed to the distorted, you know, Affan’s band kind of vibe. But I think you can still feel some of that stuff in there.”

Caleb explained the song’s meaning to The Music Fix: “It’s called ‘Mary’ and it’s M-A-R-Y, but I’m actually talking about marriage. I said, ‘Marry if you wanna. I waive my right.’ I think that was when I was kind of disgruntled about Nathan moving out of the house and getting married.
Then, in the second verse, I talk about Nacho, and I say, like, ‘We’ll dance like we’re boyfriends in sheer delight,’ because me and him used to go out and party. On this album, we were experimenting a little more and wanted to show our countrier side at times and our throwback side and wanted to give people like a brief history of what Kings of Leon have been trying to achieve all the while.”

Mary by Kings of Leon - Songfacts — Songfacts

Mary by Kings of Leon song meaning, lyric interpretation, video and chart position