The One Direction star was promoting his first solo single, This Town, on the programme when host Ellen decided to play a speed-fire Who'd You Rather? dating game.
Posting up photos of a series of celebrity beauties, she asked Niall to pick one girl to date over another.
After picking Rihanna over bandmate Harry Styles' ex-girlfriend Taylor Swift and stars like Demi Moore and Selena Gomez, he then settled on Ellie over Kendall Jenner, Jennifer Lopez and Rita Ora, prompting the host to name her the winner, adding, "If Ellie's watching, there's your guy".
Goulding briefly dated Niall in 2013 and the former couple has remained friends.