Millar was born in Toronto and raised in Brampton and Oakville. He moved to England at the age of 13 for footballing purposes. His father played for Charlton Athletic and is an electrician who works on television series, including Game of Thrones.
Club career
Early career
Millar began his career with Brampton Youth SC at the age of four. After two years he joined North Mississauga SC and remained at the club until his move to England. He joined Fulham at the age of 13 but felt he struggled to adapt to English football. On moving to England, Millar said "It took me a while to adjust to how English football is, it probably took me a good two-and-a-half years."
Liverpool
In July 2016, he joined Premier League club Liverpool on a free transfer with striking options limited in the Academy. Millar scored four minutes into his Liverpool U18s career and marked his debut in the U18 Premier League with a hat-trick in a 4–0 victory against Blackburn Rovers U18s in August 2016. A month later, he signed a professional contract on his 17th birthday. Injury ruled Millar out for three months of his inaugural season but a return in January saw him finish the season with six goals in 17 appearances in the U18 Premier League. He featured in every game of Liverpool's 2017–18 UEFA Youth League campaign and scored twice in eight games. After 18 months under the guidance of Steven Gerrard in the Under-18s, Millar received his first call-up to the Under-23 squad in January 2018.
On January 31, 2019, Millar signed a long-term first-team contract with Liverpool and joined Scottish Premiership side Kilmarnock on loan until the end of the 2018–19 season. He made his debut on February 1 in a 2–1 loss to Heart of Midlothian. He scored his first goal on March 11 against St Mirren. He returned on loan to Kilmarnock in August 2019. This loan period was cut short in January 2020 when he returned to his parent club.
Return to Liverpool
He made his senior Liverpool debut on February 4, 2020 starting in the FA Cup fourth-round replay against Shrewsbury Town. In the mid-2020 Liverpool turned down multiple transfer offers for Millar, who received loan interest from clubs in the Championship and Bundesliga.
In March 2018, Millar was named in John Herdman's first squad as national team manager. In that same camp, Millar made his senior debut and first start for Canada during a 1–0 win over New Zealand, impressing while doing so. In May 2019, Millar was named to the 23-man squad for the 2019 CONCACAF Gold Cup.
Playing style
Millar's preferred position is as a number nine, but he has been utilised in various roles with Liverpool due to his flexibility. He has been noted for his ability on the left flank. In August 2016, manager Neil Critchley said: "He's a goalscorer. He can run down the side of defenders, he runs in behind, he gives them real problems with his movement and he's a good finisher off both feet. He's got a good brain, good awareness, very calm and can finish. He's a good player, a good all-round player."
