On 21 November 2016, Scannell was added to the senior Ireland squad for their 2016 end-of-year rugby union internationals fixture against Australia. On 23 January 2017, Scannell was named in the Ireland squad for the opening two rounds of the 2017 Six Nations Championship and he was also selected in the squad for the 2017 Summer Tour against the United States and Japan. On 10 June 2017, in the one-off test against the United States, Scannell made his debut for the senior national team, converting two tries in Ireland's 55–19 win in the Red Bull Arena, New Jersey. When he took to the field, Scannell and his brother, Niall, became the first Munster siblings to represent Ireland in the professional era. A week later, Scannell made his first start for Ireland, doing so against Japan in Shizuoka Stadium, Shizuoka and scoring two points in his sides 50–22 win.