In 2014 Sewell wrote and featured on Kygo's hit, "Firestone". The single was a top five hit across Europe. His debut single "Hold Me Up" was written and produced by Brian Lee, The Euroz and Louis Bell. On 2 March 2015, Sewell announced his opening slot on Ed Sheeran's Australian tour via a video posted on his Facebook page. He joined Sheeran on 13 dates throughout Australia. On 12 June 2015, Live Nation confirmed that Sewell would join Maroon 5 on the Maroon V Tour in September as well as posting several tour dates. Sewell supported Jess Glynne on her "Ain't Got Far to Go" UK tour in October and November 2015. In October, Sewell announced that his debut extended play, All I Know would be released on 13 November 2015. He also posted various Australian and New Zealand tour dates throughout November. In March 2015, he was picked as Elvis Duran's Artist of the Month and was featured on American TV network NBC's Today show hosted by Kathy Lee Gifford and Hoda Kotb and broadcast nationally across the United States where he performed live his single "Start Again". In November 2015, at the ARIA Music Awards of 2015, Sewell won Song of the Year for "Start Again". In February 2016, Sewell released "Remind Me" as the final single from All I Know. The following month, Coca-Cola released a song and video for their new campaign, "Taste the Feeling". It features Sewell's vocals and production from Avicii.