Seattle Slew was sired by Bold Reasoning and his dam was My Charmer. He was born on February 15, 1974 and foaled at Ben Castlemans White Horse Acres Farm near Lexington, Kentucky. Seattle Slew was sold to Karen and Mickey Taylor of White Swan, Washington.
He made his first start in a six furlong maiden race on September 20, 1976 and won by five lengths. Seattle Slew only started twice more as a two year old, winning an allowance race on October 5, and the one mile Champagne Stakes eleven days later by 9 ¾ lengths. Even though he had only raced three times he was named Champion Two Year Old of 1976.
In his first three year old race he set a seven furlong track record at Hialeah Park Race Track in winning an allowance race by nine lengths. On March 26 he won the Flamingo Stakes by four lengths. Then on April 23 he scored a 3 ¼ length victory in the Wood Memorial Stakes.
On the May 7 Kentucky Derby he was ridden by Jean Cruget and won by 1 ¾ lengths. Two weeks later in the Preakness Stakes he won by 1 ½ lengths. Then he won the Belmont Stakes by four lengths in front of a large enthusiastic crowd. He became the tenth winner of the U.S Triple Crown and the first Triple Crown winner to finish the series undefeated.
Then he was sent to Hollywood Park Racetrack for the Swaps Stakes. He tired badly and ended up finishing fourth. Rest and physical problems sidelined him for almost a year. He was honored as champion three year old and the eclipse Award for American horse of The Year.
In early 1978 he was stabled at Hialeah and was expected to make three starts in Florida. But in January he took a turn for the worse. He stopped eating, occasionally broke into hours long sweats and sometimes fell when he tried to stand. His owner diagnosed him with a serious viral infection and feared for his life.
In May he made it back to the races and won an allowance race at Aqueduct by 8 ½ lengths. The he won another allowance race at Saratoga Race Course in August. But then in a major upset he lost the Paterson Handicap. In the Marlboro Cup Seattle Slew beat 1978 Triple Crown Winner Affirmed by three lengths. Two weeks later he won the Woodward Stakes. In October he met Affirmed again and lost by a nose to Exceller who had managed to keep up with his blistering pace. His last race was a victory in the Stuyvesant Handicap in November at Aqueduct Racetrack.
He retired with 14 wins in 17 races and earnings of $1,208,726. Seattle Slew was named Champion Older Horse of the Year in 1978, and was elected to the National Museum of Racing and Hall of Fame in 1981. He stood sire at Spendthrift Farm in Lexington and later at Three Chimneys Farm in Midway. He was the leading sire of 1984, and enjoyed success as a sire.
25 years to the day after he won the Kentucky Derby he died in his sleep. Seattle Slew was buried in a courtyard at Hill n’ Dale Farms near Lexington, Kentucky.