The Irish singer began dating 20-year-old aspiring model and actress Amy Green after they met in a London nightclub back in October.
However, Horan has now called time on their romance because he is too busy with his pop career to be in a relationship.
A source told the Sunday Mirror: "Sadly, it is over between Niall and Amy. He finished it because he didn't have enough time with everything he has to do.
"Understandably she was disappointed because she had been in a relationship before she started seeing Niall and chose him over her boyfriend. But there are no real hard feelings and they're still close."