Smith-Milner was born and raised in Auckland, where he attended Rosmini College and played junior basketball for Waitakere.
NZNBL and Australian state leagues
Smith-Milner started his professional career in 2012 with the championship-winning Auckland Pirates in the New Zealand NBL. He joined the Super City Rangers in 2013 but did not play, going on to make his debut for the Rangers 2014 and averaging 12.7 points per game.
After a season in the United States playing college basketball for Polk State College in 2014–15, Smith-Milner re-joined the Rangers for the 2015 season.
In 2016, Smith-Milner played for the Sandringham Sabres in the SEABL. In 2017, he played for both the Canterbury Rams in the New Zealand NBL and the Frankston Blues in the SEABL. He played for the Nelson Giants in the New Zealand NBL in 2018 and the Kilsyth Cobras in the NBL1 in 2019. In 2020, he was acquired by the Auckland Huskies. He joined the Wellington Saints in 2021.
In 2015, Smith-Milner moved to Australia to play for Melbourne United in the Australian NBL. He spent three seasons as a development player before signing a full-time contract with United in 2018.
National team career
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. The following year, he was a member of the bronze-medal winning Tall Blacks squad at the 2018 Commonwealth Games. In 2019, he played in the FIBA Basketball World Cup in China, where he averaged 5.2 points and 2.8 rebounds.