Having featured in the warm-up games against Munster and Leinster development sides, Campbell was selected in the
Ireland under-20s squad for the
2022 Six Nations Under 20s Championship when it was announced in January 2022. He made his competitive debut for the under-20s in their tournament-opening 53–5 win against
Wales on 4 February, though Campbell had to leave the field due to an injury during the first-half. That injury did not prevent Campbell from starting in Ireland's 17–16 away win against
France one week later, the 39–12 win against
Italy on 25 February, the 42–27 away win against
England on 12 March, and the 59–5 home win against
Scotland on 20 March that secured a
Grand Slam for Ireland. Campbell was initially ruled out of the Under-20s Summer Series due to a thumb injury and was not selected in Ireland' squad, however, he recovered faster than anticipated and only missed the opening fixture against
France, returning to start against
South Africa on 29 June 2022 and played the full 80 minutes in Ireland's 33–24 defeat, before also starting in the 37–36 win against
England on 5 July and the 41–24 win against
Scotland on 12 July in Ireland's final match of the series. ==Honours==