The year after her graduation, McCully became a secretary to Marion V. Langzettel, who directed the Froebel League's school for children in New York City on East 71st Street and within a few years, began working at Andrews, Davis & Platt. She began her career as an advertising copywriter at
Lord & Taylor's in New York City. McCully then became a food editor at
Bloomingdale's, where she worked from 1947 to 1960. Afterward, she served as the food editor for ''
McCall's magazine for seven years and then spent ten years as food editor for House Beautiful''. By 1960, McCully had become an icon in the food industry, bringing noted chefs together, serving as a mentor, a contact with peers, and hosting regular culinary salons in her Upper East Side apartment. Though she had a somewhat abrasive manner, McCully was very influential counting among her friends both American and foreign chefs.
Helen Evans Brown and
James Beard were close friends and colleagues. While running the kitchens for ''
McCall's magazine, she allowed Beard to use the kitchens for his cooking school and helped many chefs gain notice. When Julia Child first envisioned writing articles on French cooking and publishing cookbooks, McCully told her that though the recipes were well constructed, they would seem overwhelming to most cooks. When Child finally agreed that the recipes must be simplified, she still had trouble finding a publisher. McCully read the manuscript for Mastering the Art of French Cooking'' and gave it to
Jacques Pépin, for whom she had become a surrogate mother, telling him she thought it had merit. Pépin had only been in the United States a few months, when he met McCully through
Craig Claiborne, the noted food editor of the
New York Times and she took him under her wing. Pépin was impressed with Child's manuscript, McCully invited her over to dinner for the two to meet, and a life-long collaboration and partnership emerged. McCully was interested in making food preparation practical for busy women and, as did most food writers of her time period, advocated for the use of convenience foods. But, she also recommended trying new types of foods, advocating
Chinese food, despite the overall
xenophobia and
anti-communist sentiment common in her era. Besides her editorial work at magazines, she published several cookbooks. Perhaps her best known were
Cooking with Helen McCully beside You (1970), which was recommended by the
Chicago Tribune,
The Other Half of the Egg (1967), written with Pépin and
The American Heritage Cookbook (1967), which she edited with Eleanor Noderer, an associate from her days at ''McCall's
. The latter was praised not only for its recipes, but for its inclusion of the history of the development of the food industry in America, which was omitted from later editions of the book. A two-volume set, Nobody Ever Tells You These Things about Food and Drink
(1967) and Things You’ve Always Wanted to Know about Food & Drink'' (1972) gave practical tips, laced with humor, amid the recipes and included conversions from
U.S. measurements to
metric, translations for cooking definitions from French, as well as buying guides. McCully strove to make cooking accessible to anyone who wanted to learn the techniques, giving lectures and demonstrations and at one time, even discussed with James Beard the possibility of teaching cooking classes via correspondence course. She also published an autobiographical children's tale about the year that her mother bought her and her siblings a pony for Christmas.
The Christmas Pony (1967) was written in collaboration with Dorothy Crayder. In 1967, McCully, along with Dorothy Drayder, and illustrated by Rober J. Lee published The Christmas Pony with The Bobbs-Merrill Company, Inc. The Christmas Pony was a true story about her Christmas of 1912 when her mother got for her and her two siblings a pony. The book is dedicated to the memory of her parents. ==Death and legacy==