The former Smiths star provided the guitar to the breathtaking track, which also features an orchestral arrangement by Hans Zimmer, and revealed he was thrilled that the 18-year-old pop superstar was chosen for the gig.
Speaking on the red carpet at the BRIT Awards at The O2 in London on Tuesday night (18.02.20) - which saw the trio perform the track live for the first time, along with Billie's brother Finneas O'Connell - Marr said: “We were already working on the film when I heard Billie had done the song and that was already a good idea to me.
“Before I’d even heard the song, I thought it was just a smart idea and this was before all the Grammys and stuff.”
The 56-year-old rocker insisted it was a "very brave" move to make the song a "minimalist" ballad, but said they made sure to "Bond-ify it" without being "bombastic".
He explained: “When I heard the song, I thought ‘this is fantastic’. It’s very brave, being very minimalist. It’s her sound, and then the trick was to Bond-ify it.
“It was already a great song, but from a sound point of view, to Bond-ify it without doing the obvious.
"It’s really easy to be bombastic, so it was a case of less is more, and making it work with the film.”
The 'How Soon is Now' star heaped praise on the 'everything i wanted' singer, haling her a "really good musician"
He gushed: “Billie’s just the best new, I don’t wanna say pop act, but it’s great when someone that cool is that popular, individual and a lot of people can relate to her.
"She’s a really good musician, and her family is a really musical family, very soulful. I know a great musician when I see one.”
Marr also admitted it was a "super thrill" to work on a 007 movie and admitted he felt it was important to have guitar on it to honour the late James Bond composer John Barry's legacy.
He added: “Growing up as a British boy in the late 60s, 70s, 80s, to me, the Bond theme should have guitar in it – especially the John Barry stuff.
“The sound of it to me, the guitar riff. It’s a super thrill to do it.”