*Club domestic league appearances and goals, correct as of 17:19, 29 December 2024 (UTC) ‡ National team caps and goals, correct as of 22:06, 18 November 2024 (UTC)
Part of the youth system at Celtic since the age of eight,[3] Ralston made his debut for the first team on 11 May 2016, in a 2–1 defeat against St Johnstone.[4] He scored his first goal for the club in a 5–0 Scottish League Cup win over Kilmarnock on 8 August 2017.[5] He made further appearances early in the 2017–18 season, including a UEFA Champions League match against Paris Saint-Germain,[6] but then suffered a knee injury in late September.[7] Ralston signed a long-term contract with Celtic in December 2017, with the deal due to run until the end of the 2021–22 season.[7]
On 16 March 2018, Ralston joined Dundee United on an emergency loan until the end of the 2017–18 season, a side challenging for promotion from the Championship up to the Premiership.[8] He made his debut on 20 March, in a 3–2 loss in the league to Queen of the South.[9] In 15 appearances, he helped United reach the semi-final play-off for promotion, scoring two goals, albeit the side lost to Livingston in the semi-final play-off.[9]
On 2 September 2019, Ralston moved to St Johnstone on a season-long loan.[10] Upon his return from the St Johnstone loan, Ralston played in only one game for Celtic during the following season, coming in a 0–0 draw against Livingston when several squad regulars were missing due to a Covid-19 isolation issue,[11] and when centre-half Kristoffer Ajer then loanee Jonjoe Kenny were selected at right-back ahead of him following the sale of Jeremie Frimpong, it appeared his time with the club would be coming to an end.[12]
On 15 December 2021, Ralston headed in a 97th-minute winner against Ross County in a 2–1 away victory for a Celtic side that had been reduced to ten men.[16] It has been assessed as one of the most important moments of the season for Celtic as they went on to win the 2021-22 Scottish Premiership title, as the result kept them within touching distance of Rangers who were four points ahead in the table at that time.[17] At the end of 2022, Celtic signed Canadian Alistair Johnston who quickly became the first-choice right-back, with Ralston's role becoming that of a dependable back-up.[18]
On 26 September 2023, Ralston signed a new four-year contract with Celtic, keeping him at the club until 2027.[19]
International career
Ralston was involved with several Scotland youth squads up to the under-21s.[20]
On 7 June 2024, Ralston was named in Scotland's squad for the UEFA Euro 2024 finals in Germany.[31] A week later, he started the opening match of the tournament, where Scotland lost 5–1 to hosts Germany.[32] He went on to start in both the second match against Switzerland and the third against Hungary as Scotland finished bottom of Group A with one point from three matches.[33][34]