He played junior football for the Geelong Falcons in the TAC Cup and Victoria Country at the AFL Under 18 Championships.

He was selected as a late replacement for St Kilda captain Nick Riewoldt who pulled out due to a calf injury.

[5] Playing for St Kilda's VFL affiliate club Sandringham in June 2017, McCartin suffered a further concussion.

He was delisted by St Kilda at the conclusion of the 2019 AFL season to allow him to deal with complications resulting from repeated concussions.

St Kilda head of football Simon Lethlean stated that the club would be open to re-adding McCartin to their list after a break in 2020.

In Round 4 of the 2023 AFL season McCartin, whilst fighting for a ground ball, grazed his head on the grass causing him to be concussed.

This raised the conversation between the media and football critics such as Leigh Montagna on whether playing footy is worth causing longterm concussion problems for McCartin.