Hailing from Ballyclare, Northern Ireland, Paddy was playing for his boyhood club, Ballyclare Colts, when he was discovered by Manchester United at the age of 12 and started travelling to train with the Red Devils during his school holidays.

Penning a first deal at the club in 2011, Paddy made his professional debut as a teenager in the Premier League, starting in a 2-1 win over West Ham United in 2014.

Making 24 top-flight appearances for Man Utd, the Northern Ireland international moved to north-east neighbours Sunderland in June 2018, signing a four-year deal.

He chalked up 28 showings for the Black Cats during his two seasons on Wearside, ending the 2017/18 season in impressive goalscoring form, bagging four goals in his last five games.

Representing his country at U17, U19 and U21 level and equally adept playing in the heart of defence or midfield, Paddy helped the Northern Ireland senior team reach the European Championships for the first time in their history in 2016 and he continues to be an integral part of the squad.

Joining Boro in June 2018, on a four-year deal, Paddy made his Boro debut in a 3-0 home win against Sheffield United with his first goal for the club coming in a 1-1 draw with Millwall the following month.

Paddy scored twice for Northern Ireland in a shock 3-2 win against the Czech Republic in Prague in October 2019.

Paddy scored again for Boro at Nottingham Forest in December, but four days later was shown the first red card of his career in a 3-1 defeat at Swansea City.

He would score three more in the 2019/20 season, one in a 2-2 draw with Derby County before winners away to Charlton Athletic and Sheffield Wednesday on the final day of the season.

Returning to a centre-back role, Paddy was one of Boro's outstanding performers in the 2020/21 season and he was rewarded with a new contract which he signed in early December 2020.

Paddy was named Boro’s Player of the Year in 2021.