In the early days the club played on Blackheath Common and after the formation of Blackheath RFC in 1858, shared a dressing room with them in the Princess of Wales hotel in 1862. At that time the rules were decided before each game by the captains. As a founder member of the Rugby Union in 1871, Guy's contributed to the basic structure of the game as it is now played.

From 1920 to 1930, Guy's fielded the most formidable team in the land and the reputation achieved during that decade lingers to this day. The club has created 34 international players, the first in 1872 and the last in 1970. Guy's has won the United Hospitals Challenge Cup (the first and oldest rugby cup competition) 32 times. St. Mary's have now won the cup 35 times.

The rugby club was established at St Thomas' Hospital in 1864 but it is likely in view of the close proximity of the two "Borough Hospitals of Guy's and St Thomas'" at Southwark, that the game of football, as it was then called, was played at St Thomas' during this period 1843 to 1864.

St Thomas' first played on Clapham Common, using the Clock Tavern as its changing room. It then used Lambeth Palace Grounds until 1897, when it moved to Chiswick, and then in the 1950's to Cobham.

St Thomas' first won the Hospitals Cup in 1878 and went on to win it on a further 15 occasions; the most successful run being six consecutive wins between 1892 and 1897. The Club has produced 12 international caps; the first being J H Dewhurst playing for England in 1887-1890 and the most recent being M A Smith, capped in 1970 for Scotland. Additionally 18 club members have played for the Barbarians.

In 1982 the Medical School's of Guy's and St Thomas' Hospitals merged following over a hundred years of separate teaching, due to a fight between students of the respective hospitals breaking out in the middle of an operation, forcing the operation to be cancelled (the fate of the patient involved is unfortunately lost in the mists of time!). This merger created the United Medical and Dental Schools (UMDS) and this in turn led to the eventual merger between Guy's and St Thomas' Hospital Rugby Clubs in the early 90's. This merger of the medical schools persisted for some 17 years until, in 1999 King's College London merged with UMDS to create Guy's, Kings and St. Thomas' Schools of Medicine, Dentistry and Biomedical Sciences, leading to the creation of a GKT Rugby team, which although sporting a new name and new colours retains many of the traditions of it's constituent institutions.

Now in its 166th year, the club fields two teams in the BUCS student leagues South-East 1A and 4B, and four men's teams in Kent 1 and the Kent Metropolitan Leagues. Additionally, the club continues to fight it out for the crown of the United Hospitals cup every March in the hope of toppling Imperial Medicals RFC from their status as reigning champions. Whilst some of the grandeur and regard of the club that once existed has faded with the mists of time, the members of the club still hold a fierce pride for the status of the club as the oldest in the world and uphold the traditions of medics rugby with gusto. Rugby has been played well at GKT RFC since the organised form of the game began, and this trend looks set continue with the future of quality rugby at Guy's never in doubt.