The One Direction star has sported blonde locks since he started in the boy band.
But as he attended the Larry King Hairdressing Salon's launch party, Horan showcased significantly darker tresses.
The 23-year-old singer's hair was artfully styled into a tousled crop, and perfectly matched his stubble. Horan teamed his new look with a casual ensemble of jeans, a grey T-shirt and shearling-trimmed jacket.
While Horan beamed with delight as he debuted the new do, fans were somewhat divided by his changed appearance, reported Billboard magazine.
Some approved of the alteration, with one tweeting, "Not that Niall Horan wasn't amazing looking anyways but his brown hair is BEAUTIFUL," and another added, "Sorry, but Niall Horan looks much better and sexier with brunette hair. I hope it stays this way for a long time @NiallOfficial."