Smith-Milner was born and raised in Auckland,[1] where he attended Rosmini College and played junior basketball for Waitakere.

[2] Smith-Milner started his professional career in 2012 with the championship-winning Auckland Pirates in the New Zealand NBL.

[13] On 13 August 2021, Smith-Milner signed a two-year deal with the South East Melbourne Phoenix, with the second year being a Club Option.

[18] Smith-Milner played for the New Zealand Tall Blacks in the 2017 FIBA Asia Cup in Lebanon, where he averaged 10.5 points and 4.2 rebounds.

[19] The following year, he was a member of the bronze-medal winning Tall Blacks squad at the 2018 Commonwealth Games.