Born in the Toronto suburb of Scarborough, Miller is of Jamaican and Trinadadian descent.[3] He began playing youth soccer at age four with Malvern SC.[4] Afterward, he played with North Scarborough SC and Vaughan Azzurri.[5]
On January 11, 2019, Miller was selected 27th overall in the 2019 MLS SuperDraft by Orlando City.[13] He officially signed with the club on March 1, 2019[14] and made his professional debut appearance the following day, starting in Orlando's season opener, a 2–2 draw with New York City FC.[15] As part of Orlando's end-of-season roster decisions it was announced Miller had his contract option for the 2020 season exercised.[16]
CF Montréal
Miller was selected by Austin FC in the 2020 MLS Expansion Draft[17] and immediately traded to the Montreal Impact in exchange for $225,000 in General Allocation Money and a first round pick (11th) in the 2021 MLS SuperDraft.[18] He made his debut for Montreal on April 17 against Toronto FC. After a strong start with Montreal, the club announced on July 12 a contract extension until 2023.[19] Miller scored his first goal for his new club on November 3, scoring the second in a 2–0 win over the Houston Dynamo.[20]
As a result of Miller's strong play for Montreal during the 2022 MLS season, in July 2022 the league announced him as one of the commissioner's picks for the 2022 MLS All-Star Game.[21]
Inter Miami CF
On April 12, 2023, Miller was traded by CF Montréal to Inter Miami CF with $1.3 million in General Allocation Money for Bryce Duke and winger Ariel Lassiter.[22] He made his Miami debut on April 22 against the Houston Dynamo.[23] In October 2023, Miami announced that they had signed Miller to a contract extension through the 2026 season, with a club option for 2027.[24]
Portland Timbers
Ahead of the 2024 season, he was traded to the Portland Timbers for $625,000 in general allocation money, an international roster spot, plus another $150,000 GAM in performance-based incentives.[25]
On March 18, 2019, he received his first senior call-up for Canada for their final CONCACAF Nations League qualifying game against French Guiana.[27] In June 2019, Miller was selected in Canada's 2019 CONCACAF Gold Cup squad and made his senior international debut on June 23, entering as a 61st minute substitute in Canada's final group stage match, a 7–0 win over Cuba.[28] In July 2021 Miller was called up to represent Canada at the 2021 CONCACAF Gold Cup.[29]
In November 2022, Miller was named to Canada's squad for the 2022 FIFA World Cup.[30] He played every minute of the team's run in Qatar, as they were eliminated in the group stage.[31]