Bred by Edward B. Benjamin in Greensboro, North Carolina, the bay colt was born with a noticeably crooked foreleg, so was considered to have no future in racing. He was sold as a yearling for $1,200 at the Keeneland Sales to Venezuelan breeders Ramon Echegaray and Luis Navas. Purchased by Edgar Caibett, the horse was shipped to his owner's native Venezuela, where he earned an undistinguished record racing as a two-year-old in La Rinconada Hippodrome.
Triple Crown races
Because of his breeding, Cañonero II qualified for the Kentucky Derby, the most prestigious event in United States Thoroughbred horse racing. Trained by Juan Arias and ridden by jockeyGustavo Avila, in the spring of 1971, the horse was shipped to Louisville, Kentucky, for the big race. There, Cañonero II was dismissed as a horse that did not belong in such elite company and was listed at the bottom of the pack of the betting odds as part of a six-horse pool.
In the Derby's 20-horse field, Cañonero II shocked everyone by coming from 18th place to storm past the competition, easily winning the race by 33⁄4 lengths. Arguably the most astonishing upset in the race's history was deemed a fluke by many of horse racing's experts, who predicted Cañonero II would never win another race. However, in the Preakness Stakes, the second of the Triple Crown races, Cañonero II won again.
The third leg of the Triple Crown, the Belmont Stakes held near New York City, was run before the largest crowd in its history. The stands were filled with members of the city's large Latino community, there to cheer on their new hero. However, due to a foot infection that had bothered the horse for several days, Cañonero II, after taking the race lead, struggled across the finish line in fourth place. Despite this loss, he was named the winner of the 1971 Eclipse Award for Outstanding Three-Year-Old Male Horse.
Later career
Sold to the King Ranch, Cañonero II was nursed back to health by Hall of Fame trainer Buddy Hirsch. The following year in the Stymie Handicap at Belmont Park, he set a track record while defeating the great three-year-old champion Riva Ridge.
Retired to stud at the end of 1972, Cañonero II died in 1981.