He collaborated with Taylor Swift on her fourth album "Red", doing a duet with her on the song "Everything Has Changed". He has also written songs for One Direction. He wrote the song "Moment" and gave it to One Direction in 2011. He co-wrote two songs that were on their second album "Take Me Home". He first gave them the song "Little Things" that he had written with his friend Fiona Bevan when he was 17 years-old. As well as this, co-wrote the song "Over Again".