His family confirmed the news on Saturday morning.
"I was just throwing things out there and hoping that anything sticks," the Fleabag star joked.
Eilish and her team join a list of musical luminaries to write a theme song for a Bond movie, including Paul McCartney, Madonna, Sheryl Crow and Chris Cornell.
The 18-year-old is the youngest artist to ever record a track for a 007 film.
Oscar-winner Rami Malek will play the villain in the Daniel Craig-starrer, which is set to release in April 2020.
The singer told his new wife on Instagram: "Thank you babe for throwing me the most epic bond themed 30th birthday."
She isn't the new James Bond, but she's close.
The unconfirmed scoop would give the movie franchise its first black and female 007.
The Luther star spoke candidly about being disheartened by racist backlash to the idea, though he hasn't ruled it out.