Speaking to E! News, the 18-year-old singer said that she and her brother Finneas O'Connell have finished writing the piece saying: ''Yes, we've written it. It's already done. It's crazy, dude. It's a life goal, for sure.''
Eilish, who recently won five Grammys, and her brother sang The Beatles' Yesterday during the Oscars' In Memoriam segment on Sunday night.
The singer said that winning multiple Grammys hasn't sunk in yet: ''It's crazy. I don't know what to say to that. I don't know. It was surreal and it's still surreal. Every time I see that picture...I don't believe it.''
Eilish is the youngest person ever to write and record a Bond song and she follows in the footsteps of artists including Adele and Sam Smith in recording a Bond theme.
She has had a meteoric rise since the release of her debut album, When We All Fall Asleep, Where Do We Go?, last March. The album topped many end of year polls and went to Number One in 18 countries upon release.
The singer recently made Grammy award history when she became the youngest artist ever to receive nominations in all four major categories.