Falkirk Gallacher joined Falkirk as a graduate from the Forth Valley Football Academy in the summer of 2015, having played for the club's youth teams since the age of 10. He made his debut as a sixteen-year-old in a
Scottish Cup tie at home to
Fraserburgh on 28 November 2015. He made his first league start in a
Scottish Championship match against
Dumbarton on 17 December 2016. In January 2017, he was named as one of the ''
Daily Record's
and The Herald's'' Scottish footballing prospects for 2017. The latter reported that Gallacher had been scouted by
Premier League sides
Manchester United and
Stoke City, as well as Scottish club
Rangers.
Liverpool On 25 January 2018,
Liverpool signed Gallacher after a successful trial for a fee of £200,000. Gallacher made his competitive debut for Liverpool on 17 December 2019, starting in a 5–0 League Cup defeat at
Aston Villa. Liverpool had decided to play a shadow team in that match due to a scheduling clash with the
2019 FIFA Club World Cup.
Toronto FC On 14 September 2020, Gallacher joined Canadian club
Toronto FC in
Major League Soccer, on a loan until 31 December 2020. Due to the
COVID-19 pandemic, he first had to complete a 14-day quarantine, and then the club had to play out the rest of the season in the United States, due to Canadian travel restrictions, meaning Gallacher did not get to spend any time in Toronto, instead spending the entire time on the road.
St Johnstone Gallacher signed for
St Johnstone in January 2022, on a contract that was due to run until the summer of 2024.
Hamilton Academical In January 2025 he signed for
Hamilton Academical. ==International career==