Carshalton Athletic Miller progressed through the youth ranks at
Isthmian League Premier Division club
Carshalton Athletic and broke into the senior team for the
2013–14 season. On 15 April 2014, he made his debut in a 1–0 win at
Leiston. In December 2014, he was rewarded for his form and signed a part-time contract with the club. Miller appeared in every league match during the 2016–17 season. On 25 March 2017, he scored his first hat-trick in a 4–1 win against Herne Bay. His appearances attracted the attention of several Football League clubs, and in May 2017, he became a part of
Jamie Vardy's
V9 Academy. In July 2017, Miller trialled with
Sheffield Wednesday. After being an unused substitute on 26 August 2017, his run of 49 consecutive league appearances came to an end. However, he marked his return to action with a brace against
Corinthian-Casuals, an
FA Cup hat-trick against
Pagham and the opening goal in 2–1 win against
Faversham Town. On 20 November 2017, he scored his second hat-trick in a 6–2 win against
Egham Town in the
Surrey Senior Cup. He also netted all three goals in a 3–0 win against
Sittingbourne on 6 January 2018.
Hamilton Academical On 20 January 2018, Carshalton Athletic announced that Miller had agreed terms with
Scottish Premiership side
Hamilton Academical. Nine days later, Hamilton confirmed the signing for an undisclosed fee. After being named as an unused substitute on three occasions, Miller made his professional debut in a 2–0 win against
Motherwell on 10 March 2018. Miller had a successful 2018–19 season with Hamilton Academical where he finished as the club's top goalscorer. In February 2019 Hamilton Academical activated their option to extend his contract to keep him until summer 2020.
Rotherham United Miller joined
Rotherham United on 5 July 2020 on a two-year deal. On 22 August 2020, Mickel made his first start for Rotherham in a pre-season fixture scoring a header in a 3-0 win v Mansfield. Miller joined
Northampton Town on loan until the end of the 2020–21 season on 14 January 2021.
Plymouth Argyle On 27 June 2022, Miller joined
EFL League One side
Plymouth Argyle on a two-year contract. Injuries hampered his
2022–23 season, only making 12 appearances in Argyle's league title-winning campaign. He had to wait until 19 November to make his debut, as a substitute in Argyle's 2–2 draw away to
Burton Albion. On 2 March 2023, he featured in the
EFL Trophy Final for a consecutive season, this time coming out on the losing side as Argyle lost 4–0 to
Bolton Wanderers. The
2023–24 season in the
EFL Championship saw Miller feature more regularly, making more appearances by Christmas than he'd made in the entirety of the previous season. His versatility saw him deployed as both a wing-back in a
3–4–3, and as an out-and-out
left-back in a
4–3–3. He was offered a new contract at the end of the season. On 1 July 2024, Plymouth Argyle announced that Miller's contract had expired and that he would be departing the club.
Huddersfield Town On 1 July 2024, Miller signed for recently relegated League One side
Huddersfield Town on a two-year contract. == Personal life ==