Early career After playing in the lower grades at the
Newcastle Knights, Barnett joined the
Canberra Raiders. NYC side in 2014 In 2013 and 2014, he played for Canberra's
NYC team.
2015 In 2015, Barnett graduated to Canberra's
New South Wales Cup team,
Mount Pritchard Mounties. On 10 April, he re-signed with
Canberra on a two-year contract. On 3 May, he played for the
New South Wales Residents against the
Queensland Residents. In round 22 of the
2015 NRL season, he made his
NRL debut for Canberra against the
Wests Tigers. On 27 September, he won the 2015 New South Wales Cup Player of the Year award and was named at second-row in the 2015 New South Wales Cup Team of the Year. In November, after Barnett's management discovered his new Canberra contract for the next two seasons hadn't been lodged with the NRL, he opted to instead attempt to sign a more lucrative deal with the
Gold Coast Titans. However, after Canberra threatened legal action, the signed contract was discovered and lodged, Barnett returning to Canberra to honour the deal.
2016 On 8 May, Barnett played for the New South Wales Residents against the Queensland Residents for a second year in a row. On 8 June, he re-joined the
Newcastle Knights effective immediately on a contract until the end of 2017, after being released from the final two years of his
Canberra Raiders contract. He made his Newcastle debut in round 14 against the
New Zealand Warriors. He played nine games for Newcastle in his first season at the club as they finished bottom of the table.
2017 In March, Barnett re-signed with the Newcastle club on a three-year contract until the end of 2020. He made a total of 22 appearances and scored four tries for Newcastle as the club finished last on the table.
2018 Barnett played 23 games for Newcastle in the
2018 NRL season as the club finished 11th on the table.
2019 In round 11 against the
Sydney Roosters, Barnett kicked two goals, with one from the sideline, after regular kicker
Kalyn Ponga went off the field with an injury. In December, Barnett re-signed with the Newcastle club on a three-year contract until the end of 2023.
2020 Barnett played 13 games for Newcastle in the
2020 NRL season. He played in Newcastle's first finals game since 2013 which was a 46–20 loss against
South Sydney in the elimination final.
2021 Barnett played 24 games for Newcastle in the
2021 NRL season including the club's elimination finals loss against
Parramatta.
2022 In round 3 of the
2022 NRL season, Barnett was sent off for using a raised elbow on opponent
Chris Smith during Newcastle's 38–20 loss against
Penrith, and was subsequently referred to the
NRL Judiciary for an ungraded dangerous contact charge. Barnett had pleaded guilty and claimed the contact was careless, however, it was found to be reckless in nature, with a six match suspension handed down in relation to the incident. In April, Barnett signed a three-year contract with the
New Zealand Warriors starting in 2023, after gaining a release from the final year of his Knights contract.
2023 In round 19 of the
2023 NRL season, Barnett scored two tries for New Zealand in their 46–10 victory over Parramatta. Barnett played 15 games for the New Zealand Warriors in the 2023 NRL season as the club finished 4th on the table and qualified for the finals. Barnett played in all three finals games as the club reached the preliminary final stage before being knocked out by Brisbane.
2024 Barnett was selected to play off the bench for
New South Wales for game three of the
2024 State of Origin series. New South Wales would win the match 14–4 in Brisbane to claim the shield for the first time since 2021.
2025 In May, Barnett was selected to play for New South Wales in game one of the
2025 State of Origin series. On 2 June, Barnett was ruled out for the rest of the season after suffering an
ACL injury during the New Zealand Warriors' round 13 win against South Sydney.
2026 On 24 February 2026, the Warriors confirmed that Barnett would depart the club at the end of the season and would return home to Australia. On 12 March, it was reported Barnett had signed for the
Brisbane Broncos on a two-year deal commencing in 2027. On 27 March, Barnett suffered a broken thumb in a 32–14 defeat against the Wests Tigers, with his return date yet to be determined. On 16 April the Broncos officially announced that Barnett had signed a three year deal with the club starting in 2027. == Statistics ==