Scannell made his senior Munster debut on 1 November 2014, starting at inside centre against Cardiff Blues in a 2014–15 Pro12 fixture.

[5] On 14 November 2015, Scannell made his European Rugby Champions Cup debut for Munster, coming off the bench in their opening 2015–16 pool game against Benetton.

[22] Scannell earned his 150th cap for Munster in their 18–13 home win against Ulster in round 10 of the 2021–22 United Rugby Championship on 8 January 2022.

[23][24] He started in Munster's historic 28–14 win against a South Africa XV in Páirc Uí Chaoimh on 10 November 2022,[25] and signed a two-year contract extension with the province in January 2023.

[33] On 21 November 2016, Scannell was added to the senior Ireland squad for their 2016 end-of-year rugby union internationals fixture against Australia.

[36] 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.