It didn't take long for Rosario to become one of the top riders in California after arriving from the Dominican Republic in 2006. He grew up on a farm outside of Santo Domingo and decided to be a jockey after attending the races when he was 13. After six months in jockey school, he turned pro at the age of 14. Rosario was the leading rider in the Dominican Republic four times before deciding to test his skills in California. He came to the U.S. in 2006 and rode in Northern California for much of 2007.
It didn't take long for Rosario to become one of the top riders in California after arriving from the Dominican Republic in 2006. He grew up on a farm outside of Santo Domingo and decided to be a jockey after attending the races when he was 13. After six months in jockey school, he turned pro at the age of 14. Rosario was the leading rider in the Dominican Republic four times before deciding to test his skills in California. He came to the U.S. in 2006 and rode in Northern California for much of 2007. Rosario moved to Southern California late in 2007 and by early 2008 was riding stakes horses for major trainers. He moved into the upper echelon in 2009 when he finished fifth in earnings with $13 million. Rosario climbed to third place in 2010. He won his third consecutive Del Mar and Hollywood Park titles and his first Santa Anita crown in 2011.
In 2012, Rosario moved to the East Coast and quickly established himself as one of the top riders on the other side of the country.
Rosario started his 2013 season with a huge win in the $10 Million Dubai World Cup aboard Team Valor's Animal Kingdom. Shortly after, the Dominican Rupublic native picked up a mount for the 2013 Kentucky Derby with Shug McGaughy's trainee Orb, and he guided the Malibu Moon colt to a dominant win in the first jewel of the Triple Crown to earn his first win in the race. Rosario was aboard Orb for a fourth-place finish in the Preakness, and kept the mount for the Belmont Stakes where they finished third.
Rosario had another very good year in 2014, winning the Belmont Stakes on Tonalist. He also had the regular mount on 2014 champion older mare Close Hatches, winning three Grade 1 races on her that year. He ended his year with a win in the 2014 Breeders' Cup Turf Sprint on Bobby's Kitten for Ken and Sarah Ramsey and trainer Chad Brown. Overall, Rosario won 11 Grade 1 races in 2014. In 2015, he won the Breeders' Cup Filly and Mare Sprint on Wavell Avenue and added his fifth career Breeders' Cup win by guiding Tourist to victory in the 2016 Breeders' Cup Mile. He also finished second in the 2016 Filly and Mare Sprint aboard Wavell Avenue. Rosario recorded his sixth career win in the Breeders' Cup World Championships in 2017 when he closed from off the pace to win the Turf Sprint with 30.20-1 longshot Stormy Liberal. His seventh and eighth Breeders' Cup wins came the following year aboard Jaywalk in the Juvenile Fillies and Game Winner in the Juvenile, and he capped off a spectacular Breeders' Cup weekend in Louisville by guiding Accelerate to victory in the $6 million Breeders' Cup Classic, for his ninth win in the World Championships.
Rosario continued to score his share of top-level wins through 2019, taking his second Belmont Stakes Presented by NYRA Bets on June 8 aboard Sir Winston. He also picked up his 10th and 11th Breeders’ Cup wins on Nov. 2, 2019, aboard Filly and Mare Sprint victress Covfefe and Uni in the TVG Breeders’ Cup Mile. Rosario added wins 12 and 13 in the Breeders’ Cup the following year when he guided Vequist to a victory in the Juvenile Fillies and Knicks Go to a dominant win in the Big Ass Fans Dirt Mile.
In 2021, Rosario took it up a notch, leading all jockeys in earnings for much of the year heading into the Breeders’ Cup at Del Mar. His two best horses – Knicks Go and Jackie’s Warrior – racked up multiple graded stakes victories as they emerged as divisional leaders in the older dirt male and male sprinter divisions, respectively. Rosario picked up his third win in the Breeders’ Cup Juvenile Fillies on Nov. 5 aboard unbeaten Echo Zulu; it was his 14th win in the World Championships overall. He added another Breeders' Cup victory the next day, as he guided Knicks Go to the win in the Longines Breeders' Cup Classic.