Following Ringrose’s performances for the Ireland under-20s, Leinster coach Leo Cullen handed Ringrose his Pro12 debut against Cardiff Blues on 12 September 2015. He scored his first Pro14 try in his second match, a 37–13 win against Newport Gwent Dragons on 3 October. Ringrose captained Leinster in the 2020 Pro 14 Final in which Leinster defeated rivals Ulster by a scoreline of 27-5 to cap off an undefeated domestic season.

Ringrose was selected on the bench for Ireland’s historic win against the All Blacks in Chicago in November 2016, but did not take the field. He did though win his first Ireland cap a week later, starting the 52–21 win against Canada at the Aviva Stadium. In the final game of Ireland’s 2016 Autumn Internationals series, he scored his first international try in a 27–24 victory over Australia. He was named in the Ireland Squad for the 2017 Six Nations Championship and scored a try, set up by Paddy Jackson, in the second round against Italy. He scored his third and fourth tries against Japan respectively in the first and second tests played over the summer of 2017.