Selected in the Ireland under-20s squad for the 2019 Six Nations Under 20s Championship, Healy made his debut for the side when he came on as a replacement in their 34–24 win against Italy on 22 February 2019, before going on to start at fly-half in the wins against France and Wales, the latter of which secured Ireland's first grand slam in the tournament since 2007. He was retained in the under-20s squad for the 2019 World Rugby Under 20 Championship when it was confirmed in May 2019.