2007: 3-year-old season

Curlin was conditioned for racing by Helen Pitts. Unraced at age two, in February 2007 he won a seven-furlong maiden race for three-year-olds by 12+3⁄4 lengths at Gulfstream Park in Florida, after which he was purchased by a racing partnership headed by majority shareholder Jess Jackson of Stonestreet Farm. The partnership also included Padua Stables, George Bolton, and Midnight Cry Stables, Curlin's original owner. The new owners turned the colt over to trainer Steve Asmussen.^[12] Curlin went on to race at Oaklawn Park in Arkansas where in March, jockey Robby Albarado rode him to victory in the Rebel Stakes, and, in mid April, in the Arkansas Derby.^[13]

The first turn in the 2007 Breeders' Cup Classic.

Curlin was established as the morning-line favorite by Churchill Downs official handicapper Mike Battaglia at 7–2 in spite of the fact that no horse had won the Derby with only three prior starts since 1915 (Regret), and no horse had won with no two-year-old preps since 1882.^[14] He was the second betting choice when the race went off. Breaking from post 2 in a full field of 20, Curlin finished 3rd to Street Sense and Hard Spun. In the Preakness Stakes two weeks later, Curlin stumbled out of the gate and raced by the stands the first time in sixth, well off a hot early pace. As the leaders began to tire, he made a bold run on the far turn and entered the stretch four wide, opening the door for Street Sense to sneak by to his inside. With one furlong to go, Street Sense opened a length and a half lead. However, Curlin rallied to beat the Kentucky Derby winner in the final stride. His final time of 1:53.46, at the time, tied the track record set by Tank's Prospect in 1985, Louis Quatorze in 1996, and unofficially Secretariat in 1973 (Secretariat's time was later officially determined to be 1:53.00).^[15] Curlin was the even-money favorite in the Belmont Stakes. He engaged the champion filly Rags to Riches in a lengthy stretch duel and lost by a head. Rags to Riches was the first filly to win the Belmont Stakes in over a century.

Curlin was sent off as the favorite in the $1 million Haskell Invitational at Monmouth Park on August 5, 2007, and placed 3rd behind Any Given Saturday and Hard Spun, paying $2.10 to show on a fast track. The winning time was 1:48:35. Ridden by Robby Albarado, on September 30, he beat Lawyer Ron by a neck in a stretch duel in the Grade I Jockey Club Gold Cup at Belmont Park in a time of 2:01:20 with a Beyer rating of 114. As the Gold Cup is a Breeders' Cup Challenge race, the win earned him an automatic berth into the Breeders Cup Classic.

Curlin at the 2007 Breeders Cup

On October 27, 2007, Curlin went off as the 4th betting choice in the Breeders' Cup Classic held at Monmouth Park Racetrack in Oceanport, New Jersey. The condition was listed as sloppy on the main track after several days of rain. Emerging from about midpack in the field of nine, Curlin overtook pace setter Hard Spun at the top of the stretch and drew away to win the 24th running of the Classic by 4+3⁄4 lengths over Hard Spun. The race was the eighth time that a 3-year-old took the Classic. Curlin covered the 11⁄4 mile distance in 2:00.59, which is considered a fast time on a sloppy track, earning a Beyer rating of 119. By comparison, the Monmouth track record is 2:00.40 set in 1962 by Carry Back.^[16]

After his three-year-old campaign, Curlin was honored as the 2007 Horse of the Year as well as Three Year Old of the Year, defeating rivals Street Sense and Hard Spun.^[17]

Curlin repeated as the Eclipse Award American Horse of the Year for 2008, becoming only the fifth horse to do so and putting him in the company of the likes of Secretariat and Forego. He also was named the American Champion Older Male Horse for 2008.

2008: 4-year-old season

Curlin began his four-year-old campaign in Dubai at the Nad Al Sheba Racecourse, running in the Jaguar Trophy Handicap as preparation for the Group I Dubai World Cup.^[18] He defeated a field of five by 2 1⁄4 lengths under a hand ride in 2:00.60^[19][20]

Curlin was sent out as the odds-on favorite for the Dubai World Cup. Drawing post 12, he ran three-wide outside of the leaders for the majority of the race before clearing the field when they reached the straight, winning by 73⁄4 lengths. He also became the only horse in Dubai World Cup history to win from the 12th post position.^[21] His official winning time was initially listed by the Dubai Racing Commission as 2:00.15, which would have been the third fastest in the race's history behind Dubai Millennium and Invasor. However, that time has since been removed after an investigation by the DRC sparked by reports by The Racing Post that their timing experts showed multiple races on the card – including Curlin in DWC – as being slower than officially reported.^[22] The Racing Post claims that five of the six Thoroughbred races, the Godolphin Mile being the exception, went a full second slower than the official timings.^[23]

Curlin in 2008 Stephen Foster Handicap

On June 14, 2008, Curlin won his third start of the year, the Stephen Foster Handicap at Churchill Downs. He won by 41⁄4 lengths carrying 128 pounds (10 pounds more than the next highest weighted horse). On July 12, 2008, Curlin finished second, two lengths behind Red Rocks in the Grade I $500,000 Man o' War Stakes at Belmont Park. The turf race, with a field of seven, was run over the distance of 13⁄8 miles. Curlin carried 116 lbs, as did Red Rocks, while 3rd place runner Better Talk Now, a previous Breeders' Cup Turf winner, toted 120 lbs. Curlin was sent off in this maiden turf run by punters as the odds-on 2–5 favorite and a crowd of 8,428 was on hand to watch the race.^[24] On August 30, Curlin won the Woodward Stakes at Saratoga by one and a quarter lengths.^[25] However, after fast early fractions for the first mile, the final eighth of the race was run in a slower 14.01 seconds. On September 27, 2008, Curlin sent off as the 2–5 favorite and won his second consecutive Jockey Club Gold Cup, in a hand ride by three-quarters of a length over Wanderin Boy, earning a Beyer Speed figure of 111. The track was sealed and the final time was 2:01.93 was over a sloppy track.^[26]

The victory vaulted him past Cigar to become the No. 1 all-time North American money earner as defined as having at least one North American start. Curlin is the first North American runner to have earned over US$10 million.^[26] Curlin finished fourth in the 2008 Breeders' Cup Classic. Previously, trainer Steve Asmussen had expressed concern about running him in the Classic because of the Pro-Ride synthetic dirt at the 2008 host track, Santa Anita Park. Jockey Robby Albarado made what BreedersCup.com announcers described as an "early" move from near the back of the pack. Curlin blew by the frontrunners at the far turn but was overtaken in the stretch by eventual winner Raven's Pass, second-place finisher Henrythenavigator, and the late-charging Tiago.^[27]

On November 21, Curlin's owners announced that he would begin his stud career in 2009 at Lane's End in Versailles, Kentucky, for an initial fee of $75,000. Curlin was retired and paraded at Churchill Downs on November 29, 2008.

On January 26, 2009, Curlin won the Eclipse Award for older male horse of the year and for the second year in a row was named Horse of the Year. He joined Secretariat, Forego, Affirmed and Cigar as the only horses to win the award consecutively since the Eclipse Awards began in 1971.^[28]

Notable progeny

Curlin has produced 22 Grade 1 winners:^[35]

'c = colt, f = filly, g = gelding

Curlin also sired champion filly Rachel Alexandra's only son, called Jess's Dream who won a stunning maiden victory before being retired from injury to stand at stud in Ocala, Florida. He sired his first stakes winner when his colt Chess's Dream won the Grade 3 Kitten's Joy Stakes in January 2021.