Since retired to stud, Curlin has emerged as a major sire whose offspring include Palace Malice, Keen Ice, Exaggerator, Good Magic, Stellar Wind, Vino Rosso, Clairiere, Malathaat, Nest and Cody's Wish Elite Power Colt) Idiomatic (Filly).

[2] Kentucky-based class-action lawyers William Gallion and Shirley Cunningham Jr. bought Curlin for $57,000 as a yearling through their Midnight Cry Stable.

They sold controlling interest (80%) in the horse in February 2007 for $3.5 million[3] to a group composed of Jess Jackson, founder of Kendall-Jackson wines; Florida software entrepreneur Satish Sanan's Padua Stables; and George Bolton, an investment banker from San Francisco.

[4][5] On November 1, 2007, Judge William Wehr ruled the 20% interest in the colt owned by Gallion and Cunningham Jr. would be turned over to the more than 400 persons involved in the fen-phen lawsuit.

[7] On November 9, 2007, trainer Kenneth McPeek, who worked as a blood-stock agent and consultant for Midnight Cry Stable, filed suit in Circuit Court in Jefferson County, Kentucky alleging that the stable breached a contract calling for him to be paid a 5 percent finders fee commission on the purchase and selling price of Curlin and other racehorses, as well as other breeding rights.

On January 22, 2008, Senior Judge Roger Crittenden in a one-sentence statement overruled the foreclosure motion filed by the plaintiffs against their former attorneys for alleged mishandling their settlement in the fen-phen lawsuit.

The Blood Horse magazine further reported that according to attorneys representing Stonestreet Stable, they have "a first-right-of-refusal clause incorporated into the original sales agreement with Midnight Cry", should ever such a motion be ordered.

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.

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.

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.

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.

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.

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.

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.

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.

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.

[33] He was the leading sire at the 2022 Breeders' Cup with three winners on the Saturday card: Malathaat in the Distaff, Cody's Wish in the Dirt Mile and Elite Power in the Sprint.

He has 20 sons standing at stud, with Good Magic having the best success so far with two 3-year-old G1 "Classic" winners in Mage (Kentucky Derby) and Dornoch (Belmont), who happen to be full brothers.

Curlin has produced 25 separate North American Grade 1 winners as of 10/2024:[39] 'c = colt, f = filly, g = gelding Curlin also sired champion filly Rachel Alexandra's only son, Jess's Dream, (aka Taco) who won a stunning maiden victory at Saratoga before being retired due to injury to stand at stud in Ocala, Florida.