Born in Gawler, South Australia, Riley played youth football for Gawler Eagles, the FFSA NTC and Adelaide United before beginning his professional career with Adelaide United in 2016.

He made his A-League debut on 19 March 2016, as a late substitute in a goalless draw with Western Sydney Wanderers.

Adelaide were champions that season, for the first time in their history, though 17-year-old Riley did not make any further senior appearances, instead playing as a regular for the Reds’ development side.

Riley scored his first goal in Adelaide colours on what was his second A-League start, a fierce strike from outside of the box in a 2-2 draw with Wellington Phoenix in January 2017.

He first came to Europe in 2017 to join Club Brugge, though returned Down Under on loan with Newcastle Jets in December 2017 without making a senior appearance in Belgium.

Reaching that season’s A-League’s semi-finals, Riley gained international attention when scoring a scorpion kick, which was nominated for the FIFA Puskas Award.

He finished the loan spell with the Jets with five goals in a dozen appearances, featuring as the Jets lost out in the A-League’s grand final to Melbourne Victory.

The following season, Riley was loaned to Melbourne City, playing 30 times and scoring eight goals - making him top scorer, with one more than former Boro loanee Ritchie De Laet.

Part of the City Football Group consortium that also includes Manchester City and New York City, Melbourne were defeated by Riley’s former club Adelaide in that season’s finals series.

Ahead of the 2019/20 season, Riley returned home to Adelaide United in a permanent transfer. That campaign, he scored 10 league goals and three in the cup, including one in Adelaide’s victorious FFA Cup final against former club Melbourne City.

As well as taking club’s golden boot for 2019/20, Riley received Adelaide United’s Aurelio Vidmar Club Champion recognition - effectively Player of the Year - and to date is the youngest player in Reds history to do so.

On 5 October 2020, Riley was sold to newly-formed Major League Soccer franchise Charlotte FC, and was loaned to Birmingham City ahead of the 2020/21 season.

Having made his Blues debut as a substitute against Sheffield Wednesday, Riley then scored two minutes into his first start against Preston North End.

Earning the plaudits of Boro promotion-winner George Friend, who said about Riley: 'every day in training [at Birmingham] he was arguably the best player. He has got a great temperament and personality - and most of all he is a talented footballer,’ Riley quickly became a fan favourite at St Andrew’s, and his loan was extended until January 2022.

After starring for Australia’s Under-17 and Under-23 sides, Riley made his senior debut on 3 June 2021 as a late substitute in a 3-0 World Cup qualifying win against Kuwait. His first international start was a man-of-the-match performance, providing two assists in a 5–1 victory against Chinese Taipei.

As well as representing Australia at the 2020 Olympics, Riley has been capped at full international level seven times.

Riley joined Boro on a three-and-a-half-year deal in January 2022, scoring his first goal in a 1-1 draw away at Swansea City.

He then followed up by netting again four days later, in a 2-0 home victory against the Swans’ bitter rivals Cardiff City.

Riley scored the winning goal in the Tees-Wear derby in September 2022, slipping the ball underneath Anthony Patterson to extend our unbeaten run over Sunderland to seven matches.