Born in London, UK, 1 January 1892, Jacob Horwitz immigrated to the U.S. with his family when he was a child. After graduating in 1910 he opened a grocery with a friend in Manhattan. As a member of the National Guard, he was called into service in 1916 to quell Pancho Villa along the Mexican border, but when returned, the grocery business had gone bankrupt. After returning from serving in the U.S. army during World War I, Horwitz went into business again with a partner, this time making shirtwaists (blouses) and shirtwaist dresses. By 1925 they had formed the company Horwitz & Duberman.
In the 1930s, Horwitz became a pioneer in the field of Junior wear (along with department store owner Irving Sorger and French designer Jacques Heim). Until the 1930s teenagers and collegiate aged girls adjusted ready-made adult-sized dresses to fit their smaller frames, but Junior sized clothing was designed in youthful styles specifically for the smaller framed, shorter-waisted younger woman. Horwitz, who considered himself a manufacturer and stylist, not a designer, hired young women to design the clothes. His first label ‘Judy ‘n Jill’, which was in business from the late 1930s to the mid 1950s, was carried by department stores across the U.S. Another line he launched in 1939 was branded ‘Deanna Durbin’, after the popular teenaged singing actress.
Horwitz was awarded the Coty Award in 1947 for his role in creating the Junior market. In the early 1950s Horwitz bought out his partner Duberman, and the company became known as Jack Horwitz Associates. He retired from his own company by 1960, and died in 1992 at the age of 100.