[10] One week later, Casey scored his first try for Munster in their 33–6 win against Welsh side Ospreys, in what was the provinces final pool fixture of the 2019–20 Champions Cup.

[14] Casey signed a three-year contract extension with Munster in September 2022,[15] and earned his 50th cap for the province when he started in their 21–5 home win against Italian side Zebre Parma in round three of the 2022–23 United Rugby Championship on 1 October 2022.

[3] Having overcome his injury issues, Casey was named as vice-captain in the under-20s squad for the 2019 Six Nations Under 20s Championship,[18] and made three appearances, scoring two tries, during the tournament, which saw Ireland secure a grand slam victory for the first time since 2007.

Ireland captain Johnny Sexton remarked after the game that Casey's attitude reminded him of former England fly-half Jonny Wilkinson.

[40] During the 2023 Rugby World Cup warm-up matches, Casey started for Ireland in their 33–17 win against Italy on 5 August but had to leave the field with an injury early in the second-half.

[43] Casey made his World Cup debut for Ireland in their 59–16 win against Tonga in their second pool game on 16 September.

During their 2024 Autumn Nations Series fixture against Fiji, starting fly half Sam Prendergast was sin binned following a high tackle.