Rule Supreme began his racing career by finishing third in a novice hurdle race at Wexford Racecourse on 4 May 2001 in which he finished third of the fifteen runners. He returned in autumn, and was unplaced in races at Gowran Park and Down Royal before showing improved form to finish second at Navan and Punchestown. On 29 December he started 11/4 favourite for a maiden hurdle over two and a half miles at Leopardstown Racecourse. Ridden by Charlie Swan he led from the start and recorded his first victory as he won by ten lengths despite being eased down in the closing stages.[5]
Rule Supreme returned in March to finish second in novice events at Punchestown and Fairyhouse: in the latter event he was beaten five lengths by the subsequent Grade I winner Davenport Milenium. The gelding returned to Fairyhouse on 17 April for a two and a half mile novice hurdle and started 4/6 favourite against nine opponents. Ridden again by Swan, he led for most of the way and held off the challenge of Four Aces to win by a length.[6] He ended his season ten days later by finishing fourth over three miles at Punchestown.
For the 2002/2003 season Rule Supreme was transferred to the stable of Willie Mullins and was campaigned in novice steeplechases. He made only two appearances, finishing a close fourth at Leopardstown in January and fifth, beaten thirty lengths by Adamant Approach at Cork Racecourse in April.
Having failed to win two starts in early 2003, Rule Supreme was still eligible for novice chases in the 2003/2004 season which began in April. At the end of that month he carried 161 pounds in handicap race for novices over three miles and a furlong at Punchestown. Ridden by David Casey made steady progress over the last six fences before overtaking his better-fancied stable companion Hedgehunter in the closing stages and winning by three and a half lengths.[7] In the last race of his spring campaign, Rule Supreme started 4/7 favourite at Gowran Park but fell at the eighth fence when in third place.
After a break of more than six months, Rule Supreme returned at Thurles Racecourse in December when he won the Glen Chase, beating more experienced rivals by four lengths when ridden by Ruby Walsh.[8] Three weeks later he was moved up in class when he was sent to England for the Grade I Feltham Novices' Chase at Kempton Park Racecourse. Ridden by A. P. McCoy, he lost touch with the leaders in the closing stages and was the last of the three finishers behind the Paul Nicholls-trained favourite Strong Flow. In the early part of 2004, the gelding was again campaigned in handicap company and ran well without winning, finishing third when attempting to conceded eleven pounds to Hedgehunter at Gowran Park and second when conceding thirty pounds to Coq Hardi Diamond in the Grand National Trial at Punchestown.
Rule Supreme was sent to England for the second time to contest the Grade I Royal & SunAlliance Chase on 17 March at the Cheltenham Festival. He was ridden by Casey and started a 25/1 outsider for a race whose leading contenders appeared to be Our Vic (winner of the Reynoldstown Novices' Chase), Pizarro (Champion Bumper) and Royal Emperor (Towton Novices' Chase). Rule Supreme did not jump well and was towards the rear of the field for most of the way, but began to make progress approaching the second last fence where Mossy Green fell and brought down Pizarro. He overtook Old Vic after the last fence and held off a challenge from Royal Emperor to win by one and a quarter lengths.[9] After the race Mullins said "He'll probably go to Punchestown and then possibly the French Champion Hurdle, then next year we might seriously consider the Stayers' Hurdle. The ability is there for a Gold Cup, but probably not the scope for it with his jumping. He's got a tremendous engine, but is a scrappy jumper".[10] Rule Supreme returned to England again in April, unseating Casey when he made a bad jumping mistake in the Mildmay Novices' Chase at Aintree, and finishing fifth when carrying 164 pounds in the Betfred Gold Cup at Sandown Park on the last day of the season.
Four days after his defeat at Sandown, Rule Supreme started a 20/1 outsider and finished fifth of the six runners behind Beef Or Salmon in the Grade I Punchestown Gold Cup. The National Hunt season in Britain and Ireland then went into the summer break, but Rule Supreme remained active and was sent to race in France. On 30 May he was ridden by Casey and started a 41/1 outsider for the Grade II Prix La Barka over 4300 metres at Auteuil Hippodrome. Racing on very soft ground, he took the lead two hurdles from the finish and kept on after being overtaken to finish third behind Great Love and Nickname. Three weeks later he faced Great Love and Nickname again, as well as the leading steeplechasers Kotkijet and Batman Senora in France's most important hurdle race, the Grande Course de Haies d'Auteuil over 5100 metres. Casey restrained the gelding towards the back of the seven runner field before moving up to dispute the lead three hurdles from the finish. He took the lead 150 metres from the finish and won by two lengths from Great Love, with Kotkijet two and a half lengths back in third place.[11] Mullins was unable to attend, after contracting food poisoning on his previous visit to France but John Lynch, the gelding's owner was reportedly "ecstatic", saying "They said that Kotkijet was unbeatable! This shows what a great trainer Willie Mullins is. After Punchestown, Rule Supreme had a ten-day break and put on so much weight that people thought he was pregnant!"[12]
In the autumn of 2004, Rule Supreme was campaigned in long distance hurdle races, beginning with a win under top weight of 165 pounds in a handicap at Clonmel Racecourse on 18 November. He then finished third behind Solerina and Brave Inca in the Hatton's Grace Hurdle and was sent to England in December where he finished third again beaten less than a length by the French-trained Baracouda in the Long Walk Hurdle at Windsor Racecourse. He returned to steeplechasing later in the month for the Lexus Chase at Leopardstown in which he was matched against Beef Or Salmon and the three time Cheltenham Gold Cup winner Best Mate. He was disputing second place with Best Mate, some way behind Beef Or Salmon, when he fell at the second last fence.
On 6 February 2005 Rule Supreme met Beef Or Salmon again in the Hennessy Cognac Gold Cup over three miles on soft ground at Leopardstown and was made the 11/2 second favourite. Casey positioned the gelding in fourth place, moved up to third with six fences left to run and was left in second place behind Murphy's Cardinal when Pizarro fell at the next obstacle. He took the lead three fences from the finish but was soon joined by Beef Or Salmon, the 8/15 favourite. Rule Supreme regained the advantage at the last fence and drew away on the run-in to win by fourteen lengths.[13] After the race Casey said "He kept coming for me today and he was very good. The horse is very well in himself and we always knew he had the ability to win a race like this. I know he stays all day so I though I would put it up to Beef or Salmon and see what happened".[14] Mullins reiterated his belief that the gelding had "a huge engine", but admitted that "jumping is just not his forte".[15]
At the Cheltenham Festival in March, Rule Supreme bypassed the Cheltenham Gold Cup and reverted to hurdling, starting 4/1 second favourite for the World Hurdle. In a strong renewal of Britain's most prestigious race for long distance hurdlers, he was restrained by Casey in the early stages before staying on in the closing stages to finish third behind Inglis Drever and Baracouda. At Aintree three weeks later he started 2/1 favourite for the Liverpool Hurdle, but unseated Ruby Walsh after being hampered at the second hurdle.[16] On 27 April, Rule Supreme was matched against the Cheltenham Gold Cup winner Kicking King in the Punchestown Gold Cup. He finished second, three lengths behind the Gold Cup winner, but fifteen lengths clear of the other runners.
As in the previous season, Rule Supreme was sent to contest the major French hurdle races in the summer. On 29 May, he repeated his performance of 2004 by finishing third in the Prix La Barka beaten two lengths and six lengths by Rock and Palm and Cyrlight. On 18 June he attempted to win the Grande Course de Haies for a second time, but after disputing the lead for much of the way he was beaten four lengths into second place by the six-year-old Lycaon de Vauzelle.[17]
Rule Supreme missed the next two seasons with injury problems returning as a twelve-year-old in the early part of 2008. He finished unpaced behind Hi Cloy in the Grade II Kinloch Brae Chase at Thurles in January and was last of the eight runners behind The Listener in the Hennessy Gold Cup a month later.[18]
In 2009 Rule Supreme was bought by Michael Winters and competed in the amateur Point-to-point circuit. He ran ten times, winning races at Dawstown, Ballindenisk and Ballingarry.[19]