He previously played for the Dolphins, the St. George Illawarra Dragons and the New Zealand Warriors in the National Rugby League, and the Australian Prime Minister's XIII and Country New South Wales rugby league team at representative level.

[17][18] In Round 6 against the Canterbury-Bankstown Bulldogs, he scored his first NRL career try in the Dragons' 31–6 win at ANZ Stadium.

[25] In 2017, Aitken was forced to miss Scotland's 2017 World Cup campaign due to injury.

[27] In Round 21 of the 2019 NRL season, Aitken made his 100th first grade appearance and scored a try as St George defeated the Gold Coast 40-28 at Kogarah Oval.

[28] On 11 August 2020 Aitken signed a three-year deal to join the New Zealand Warriors starting in 2021.

[35] In round 7, he scored a try in the Dolphins 14-36 loss to the South Sydney Rabbitohs at Suncorp Stadium.

[38] In September, the Dolphins' Inaugural Presentation Ball was held at Brisbane Convention and Exhibition Centre, and Aitken received the club's annual Academic Award for continued study in an MBA.

[40] On 12 August 2024, it was announced that Aitken would depart the Dolphins at the end of the season and he had signed a three-year deal with the South Sydney Rabbitohs.

[41] On 22 December, Akiten would be ruled out for the first month of the 2025 season due to needing more surgery on his pec injury.