He started his senior career with Bolton Wanderers before moving to Celtic, from whom he spent two loan spells at Queen's Park.

[4] On 5 January 2019, Connell made his competitive debut in a 5–2 win over Walsall in the FA Cup Third Round as an 89th minute substitute replacing Luke Murphy.

[6] On 25 January, Connell started his first senior game in a 2–1 defeat to Bristol City in the FA Cup fourth round and assisted Mark Beevers' goal.

In May 2018, Connell made two appearances in the 2018 UEFA European Under-17 Championship group stages, playing in wins against Denmark and Bosnia and Herzegovina.

Connell featured in victories against Romania, Azerbaijan and Russia as Ireland qualified for the UEFA European Under-19 Championship.

[24] Connell made his Republic of Ireland U21 debut on 26 March 2021, playing the full 90 minutes in a 2–1 win over Wales U21 in Wrexham.