[3] He secured a pre-med course at Melbourne University which he opted to quit in favour of completing a Bachelor of Arts in film and anthropology.
[5] Gallagher began his career starring in the Nine Network children's series The Saddle Club as Ashley 'Chewie' Becker.
[3][2] That year Gallagher joined the cast of the Australian soap opera Home and Away, playing the role of Josh Barrett.
[7] The two characters appeared in their own stand-alone webisodes titled Home and Away Extras, before making their debuts in the main show.
[9] In 2016, the actor played the part of gay character Kyle in Josh Thomas' comedy series Please Like Me.
[10] Gallagher also travelled to refugee camps located in the Middle Eastern country Jordan, where he worked as a photographer for the charity Act of Peace.
[3] In 2020, he appeared as Travis Kelly in the prison drama Wentworth and he later joined the cast of the soap opera Neighbours, playing the role of Nathan Packard.
[17] Also that year he joined Netflix teen drama series Surviving Summer, playing the character Trav Morphett.
[18] In 2023, Gallagher played the role of Winston Strong in Amazon Freevee show Almost Paradise in the episode titled "Uncoupled".