Jacobs grew up in East New York, Brooklyn in New York City. As a child he raised pigeons on the roof of his tenement building where he lived and raced them. He finished his formal schooling in elementary school at the age of 13; everything he know about animal behavior and veterinary medicine was self-taught. An older friend, Charlie Ferraro, the brother of his boss, introduced Jacobs to horse racing when he took him to Jamaica Racetrack in Queens. Ferraro bought a horse for $1500 and asked Jacobs to train it.
As a youth Jacobs worked as a steamfitter's assistant, but he quit to become a "jack-of-all-trades" at the race track. On December 29, 1926 Jacobs had his first official winner, Reveillon, at Pompano, Florida. In 1927 he became a trainer with what became his life-long partner Isidor Izzy (Kid Beebee) Bieber. Bieber was a well-known gambler who was the inspiration for Damon Runyon's "Guys and Dolls."  Bieber put up the money and Jacobs trained the horses.
Jacobs was the leading race-winning trainer in the United States 1933-39, 1941–44, the U.S. leading money-winning trainer, 1946, 1960, 1965, and the U.S. leading money-winning breeder, 1964-67. During his career, he saddled 3,569 winners, more than any other until the time of his death. 
In 1958, Hirsch Jacobs was inducted into the National Museum of Racing and Hall of Fame.
Stymie was Jacobs biggest success. The horse was from the large King Ranch in Texas and was well-bred, but he was not winning until Jacobs bought him. In 1943 Jacobs purchased Stymie for $1,500 in a claiming race. By the end of Stymie's 7-year-long racing career which covered over 140 miles of racing, he had a lifetime earnings of $918,485, which was more than any other horse had earned until that time. Those earnings helped Jacobs and Bieber establish a breeding farm in Maryland, Stymie Manor. 
Family racing business
Hirsch Jacobs and his wife Ethel owned a number of horses which were raced under her name. In 1970, the Jacobs family won two of the U.S. Triple Crown races, capturing the Preakness and Belmont Stakes. They won the Preakness with Personality, who earned American Horse of the Year honors, and the Belmont with High Echelon. Both horses were owned by Ethel Jacobs and trained by their son, John. Their daughter, Patrice, became involved in the sport. She married Louis Wolfson and their Harbor View Farm owned and bred the 1978 American Triple Crown champion, Affirmed.
Hirsch Jacobs had a daughter, Patrice, and two sons, John and Tom. He had three brothers, Eugene, Sidney and Albert, and four sisters, Mrs. Irene Robbins, Miss Helen Jacobs, and Mrs. Flo Jacobson and Mrs. Lillian Gold. He died in 1970 in Miami Beach, Florida of a cerebral hemorrhage. He was buried in Gate of Heaven Cemetery in Valhalla, N.Y.  He married Ethel Dushock in 1933. He had lived with his wife in Forest Hills, Queens.
- Times, Special To the New York (1970-02-14). "Hirsch Jacobs, Leading Trainer, Is Dead". The New York Times. ISSN 0362-4331. Retrieved 2018-06-05.
- CUTLER, JACQUELINE. "Brooklyn kid trained long shot horse to become a champ in 1940s - NY Daily News". nydailynews.com. Retrieved 2018-06-05.
- Staff. "Hirsch Jacobs, Leading Trainer, Is Dead; Had More Winners Than Anyone Saddled Stymie", The New York Times, February 14, 1970. Accessed June 18, 2009.
- Hirsch Jacobs at the United States' ional Museum of Racing and Hall of Fame
- Bowen, Edward L. Masters of the Turf: Ten Trainers Who Dominated Horse Racing's Golden Age (2007) Eclipse Press (ISBN 978-1581501490)
- June 26, 1961 Sports Illustrated feature story on the Jacobs family