With rock ballad Sign of the Times, the 23-year-old follows in the footsteps of One Direction bandmates Niall Horan and Louis Tomlinson in putting out solo material in the last year.
Speaking on Britain's BBC Radio 1 Breakfast Show with Nick Grimshaw, Styles, who stars in upcoming World War Two drama Dunkirk, said he was "nervous" before introducing the track.
"It's a bit weird. I feel like I've been hibernating in the studio for so long," he said. "You hear it in the safety of the studio . . .(and now) it's time to give birth."
Upon its debut, British media were quick to draw comparisons with the late David Bowie's music. "It's the song I'm most proud of writing I think," Styles said.
The originally five-member One Direction formed on British television talent show The X Factor in 2010 and won legions of fans around the world soon after. The best-selling group was reduced to four members in March 2015 when Zayn Malik announced he was quitting the band.
A few months later, Styles, Horan, Tomlinson and fellow member Liam Payne said the group would be taking a break from early 2016.
