After completing her training, Agnes worked as a cook in various establishments. This experience refined her skills and provided valuable insights into the professional kitchen environment.

Agnes Marshall established the Marshall School of Cookery, a pioneering institution that offered classes in all aspects of cooking. It quickly became a popular destination for aspiring chefs and home cooks alike, solidifying her reputation as a leading culinary authority.

Recognizing the limitations of existing ice cream-making methods, Agnes Marshall developed and patented her own ice cream machines. These innovative devices made the process faster, easier, and more efficient, contributing significantly to the popularity of frozen desserts.

Agnes Marshall published 'The Book of Ices,' a groundbreaking cookbook dedicated entirely to frozen desserts. It contained a wealth of recipes, techniques, and advice, making it an essential resource for anyone interested in making ice cream, sorbets, and other frozen treats. The book further cemented her status as the 'Queen of Ices'.