Paddy joined Boro from north-east neighbours Sunderland in June 2018 on a four-year deal.
The Northern Ireland international came through the ranks at Manchester United, making his debut in a 2-1 win over West Ham in 2014.
He made 24 appearances for the Red Devils and moved to the Stadium of Light in the summer of 2016.
He chalked up 28 appearances for Sunderland during his two seasons on Wearside, scoring seven goals.
Representing his country at U17, U19 and U21 level and equally adept playing in the heart of defence or midfield, Paddy helped Northern Ireland senior team reach the European Championships for the first time in their history in 2016 and continues to be an integral part of the squad.