Poole made his Newport County debut at the age of 16 years on September 20, 2014 in the preliminary line-up of the Football League Two match versus Shrewsbury Town. He became the youngest ever Newport County player and earned his place for the Football League Trophy on September 23, 2014.
In October 2014, Poole was named in the Wales Under-17 squad for the matches against Russia, Belarus and Montenegro. He made his debut in the third match against Montenegro in Minsk, when he began the 2–1 win.
In February 2015, Poole was shortlisted for the Football League Apprentice of the Year award. Three months later, on May 18, 2015, he underwent a one-week trial with Liverpool.
On 1 September 2015, Newport County confirmed Poole had joined Premier League club Manchester United for an initial fee of £100,000 (potentially rising to £400,000 with future add-ons).
In November 2015 Poole was named in the Wales under-19 squad for the Euro Under-19 qualifying matches versus Georgia, Albania and Austria.
On 1 February 2016, five months after joining Manchester United, Poole received international clearance and was free to play competitive football. Poole was included in Manchester United’s squad for the knockout phase of the 2015–16 UEFA Europa League and given the number 41 shirt.