The couple were spotted sitting together in the stands at London's O2 Arena, which saw the Brooklyn Nets beat Atlanta Hawks.
Liam was sporting a David Beckham-esque hairstyle and looked smart but casual in a black T-shirt, black jeans and a grey wool coat.
Sophia, an aspiring model, was dressed in all-black, opting for a roll neck jumper and pair of leather skinny trousers.
Posing for a picture together, Liam gently rested his hand on Sophia's knee as they both smiled at the camera.
1D star Liam confirmed he was dating Sophia in August last year.
At the time, a source said: "Liam has really fallen for her. It's getting very serious, very fast. She's a sweet, normal girl who likes Liam for who he is, not because he's in the most famous boyband in the world."
Three months earlier, Liam had split with his long-term girlfriend Danielle Peazer.