Melbourne City On 21 October 2015 he made his senior professional debut for
Melbourne City in a
2015 FFA Cup match against
Perth Glory. He made his A-league debut against Newcastle Jets off the bench.
South Melbourne In February 2016, Millar left Melbourne City to return to the
National Premier Leagues Victoria, signing for reigning premiers
South Melbourne. On 19 May 2016, after 7 goals in 14 appearances, Millar extended his contract with South Melbourne until the end of the 2017 NPL Victoria season.
Central Coast Mariners In July 2018, Millar returned to the
A-League, signing a one-year contract with
Central Coast Mariners. When Millar signed with rivals the Jets he was famously told to go home upon announcing his move at training.
Newcastle Jets On 1 February 2019 it was announced Millar had signed for the
Newcastle Jets for the
19-20 A-League season. For his first season at Newcastle he started every game for the club, except the last 2 due to an injury. He played predominantly as a very attacking wing back and was their equal 2nd top goalscorer with 4 goals as well as 3 assists. During the same season he received a NAB Young Player of the Year nomination in March.
Riley McGree was the winner of the award for the season.
Shrewsbury Town (loan) On 5 October 2020, Millar joined
League One side
Shrewsbury Town on a short-term loan deal until January 2021 with an option to buy. He scored his first goal for Shrewsbury on 10 November 2020 in an
EFL Trophy group game against
Crewe Alexandra. After the club were unable to agree a deal for a permanent transfer, Millar returned to
Australia on 19 January 2021.
St Mirren On 7 September 2021, Millar moved to
Scotland to sign a 1-year contract for
St Mirren in the
Scottish Premiership.
Macarthur FC After not being able to solidify a place in
St Mirren’s starting 11, Millar returned to the
A-League Men signing for
Macarthur FC on a one-year deal. In May 2024, Millar was named in an alleged A-League bet-fixing scheme.
Istiklol On 3 August 2024,
Tajikistan Higher League club
Istiklol announced the signing of Millar on a contract until the end of the
2024 season. Millar won the
2024 Tajikistan Higher League with the club and featured in the
2024–25 AFC Champions League Two.
Havadar In January 2025, Millar joined
Persian Gulf Pro League side
Havadar. ==Career statistics==