[3] Gallagher scored his first goal for St Mirren in a 3–2 defeat against Livingston in the Scottish League Cup on 25 August 2015.

[5] He left St Mirren in January 2017, signing for Scottish Championship rivals Dumbarton on a short-term contract until the end of the season.

[7] Whilst at the Sons, Gallagher scored his first career brace – in a 3–2 Scottish Cup victory against Peterhead in January 2018.

[8] After finishing as the club's top scorer with seven for the season as Sons were relegated to Scottish League One, Gallagher signed a new one-year deal in June 2018.

[10] He was their top scorer in the 2021–22 and 2022–23 seasons, helping the club gain promotion back to the Scottish Championship via the play-offs in 2022-23.