And the One Direction pin-up celebrated in true romantic style with his new girlfriend, Sophia Smith.
The handsome duo headed out to Funky Buddha nightclub in London's swish Mayfair area.
CLICK ON PHOTOS FOR FULL GALLERY
Sophia, 19, looked smoking hot for the special occasion, wearing a satin lime-coloured ensemble and holding a black clutch in her hand. Her beautiful brunette locks were immaculately curled, and black stiletto sandals completed the sleek outfit.
The birthday boy, meanwhile, looked cool in a baseball shirt and jeans, wearing a baseball cap backwards.
To the disappointment of One Direction fans, Liam confirmed the relationship with his childhood crush at a press conference for the band's film last week.
Soon after, they made their first public appearance as a public, wearing coordinated black outfits at the after-party for This Is Us.
While the couple haven't been dating for very long, sources have said that Liam has "really fallen for her. It's getting very serious, very fast."
Earlier on in the day, Liam filmed One Direction's latest music video with fellow band mates Harry Styles, Zayn Malik, Niall Horan and Louis Tomlinson.
First thing in the morning, he thanked his fans for the last three years, saying that was the biggest birthday present he could ever have.
"Good morning everyone :) can't quite believe my life there's no bigger birthday present than what you've done for me in 3 years thank you xx."
Fellow band member Niall Horan took to Twitter to wish his "brother" a happy birthday in a heartfelt message.
"Happy birthday to my brother @Real_Liam_Payne ! No longer a teenager buddie! love you dude!" he wrote on Thursday.