[2][3][4][5][6] His father Milton Horwitz was a general manager for a coat factory, and his mother Gertrude was a homemaker and subsequently a stenographer and a bookkeeper; both of his parents were children of Russian Jewish immigrants.

[7] His hometown is Clifton, New Jersey, to which he moved at six years of age, and where he still lives in the small house in which he grew up.

There, he was a student manager of the school's varsity baseball, basketball, track and field, and cross country teams.

[12][13] Spencer said: Jay was our public relations guy for Team Israel during the WBC ... And it just kind of blew up.

[1][14] He was also a sportswriter for the Herald News of Passaic, New Jersey, where Horwitz covered high school sports and the New York Jets for three years, beginning in the fall of 1969.

[6][8] Horwitz began working for the New York Mets on April 1, 1980, initially with the title of director of public relations.

[16][18] In 2019, the New York Chapter of the Baseball Writers' Association of America gave him the "William J. Slocum/Jack Lang Award for 'Long & Meritorious Service'".

[19][20] In May 2020 Horwitz published his memoir, Mr. Met: How a Sports-Mad Kid From Jersey Became Like Family to Generations of Big Leaguers (Triumph Books), with a foreword by pitcher Jacob deGrom.

[10][14][17] Reviewing it, New York Times sports columnist George Vecsey wrote: "This sweet book shows the beating heart of a sport ..."[17] In 1998, Horwitz was awarded the Fishel Award for Public Relations Excellence in Major League Baseball.