Nidetch was born in Brooklyn, New York, to David Slutsky, a cab driver, and Mae Slutsky, a manicurist. A graduate of Girls’ High School, Nidetch received a partial scholarship to Long Island University but was unable to attend due to a lack of financial resources. Instead, Nidetch enrolled in a business course at City College of New York. When her father died in 1942, Nidetch dropped out and started working.  Nidetch’s first job was at the Mullin Furniture Company in Jamaica, New York. She later worked for Man O’War Publishing Company and the Internal Revenue Service. Nidetch met her husband at the IRS.

An overweight housewife with a self-confessed obsession for eating meat, Nidetch had experimented with numerous fad diets before, in 1961, following a regimen prescribed by a diet clinic sponsored by the New York City Board of Health. After losing 20 pounds (9.07 kg), and finding her resolve weakening, she contacted several overweight friends and founded a support group which developed into weekly classes, and incorporated on May 15, 1963, into the Weight Watchers organization.  In 1978, Weight Watchers was sold to the H. J. Heinz Company. Nidetch, who remained a consultant to the organization, established scholarship programs at the University of California at Los Angeles and the University of Nevada, Las Vegas.  She died on April 29, 2015, in Parkland, Florida at the age of 91.