He was the third child born to a Presbyterian father, Thomas Farquharson, a sanitary contractor, and a Catholic mother, Margaret Cassin, a dressmaker.
He helped the side reach the final of the Leinster Minor Cup, held at Shelbourne Park, where they defeated Olympic B 4–2.
He was described as a "non-violent member" of the Irish Republican Army (IRA), a role that included running messages for the group and transporting people to safehouses.
[6][7] A 19-year-old student at the time,[8] he was arrested along with his friend Seán Lemass, later to become Taoiseach, for pulling down British Army wanted posters in St Stephen's Green.
His performances for Abertillery led to him being invited to a trial with Cardiff by club founder Walter Bartley Wilson in February 1922 before signing permanently.
[10] The following season, Ben Davies remained first choice at the start of the campaign before Farquharson featured in five consecutive matches between October and November 1922.
The pair continued to compete throughout the season with Farquharson featuring in 21 league matches (one more than Davies) and playing in the club's 3–2 victory over Aberdare Athletic in the 1923 Welsh Cup final.
[10] His performances resulted in Davies' being sold at the end of the season to Leicester City with long-serving Herbert Kneeshaw remaining as cover.
[11] In the following campaign, Farquharson helped the side reach their first FA Cup final where they suffered a 1–0 defeat to Sheffield United.
[10] With the retirement of Kneeshaw, Farquharson saw off competition from Joe Hills and Tommy Hampson to continue his spell as first choice goalkeeper.
[4][6] Wilson later described the incident, remarking "I thought I was seeing things when I looked at Tom Farquharson in the Cardiff goal.
"[13] Farquharson explained the reasoning behind his technique, stating "By advancing forward I can leap to either side far more quickly than from a standing position.
"[13] In the final of the competition, Cardiff defeated Arsenal 1–0 at Wembley Stadium, becoming the only non-English side to have won the FA Cup.
A board meeting was hastily arranged during which Farquharson agreed to remain with Cardiff,[16] where he played for a further three years before retiring in 1935.
[4] In his book, The Who's Who of Cardiff City, Dean Hayes describes Farquharson as "without doubt [...] the greatest goalkeeper in the history of the club.
Soon after, he also appeared for a Welsh League XI against their counterparts from the Irish Free State at Dalymount Park, suffering a 3–1 defeat.
[4] The highlight of his appearances for the FAI XI came on 26 April 1931 when he helped them hold Spain to 1–1 draw in the Montjuic Stadium in Barcelona.
Farquharson was believed to have carried a handgun in his kitbag during his playing career "for protection" following his involvement with the IRA in his youth.
"[19] Eddie Jenkins also recalled an incident when Farquharson was annoyed by teammate George Russell, who he believed was showing off, and produced the weapon before he tongue-in-cheek "threatened to shoot him if he didn't behave".
[20] Farquharson and his family lived on Allensbank Road in Heath, Cardiff, before later moving to Cyncoed in the northern part of the city.