Lillian began collaborating with her husband, Frank Gilbreth, on time and motion studies, applying psychological principles to improve workplace efficiency. Their partnership revolutionized industrial engineering practices.

Frank published 'Motion Study' (written in collaboration with Lillian), one of the first major works on the subject, introducing the principles of breaking down tasks into fundamental motions (therbligs) to optimize performance.

Lillian earned a Ph.D. in Psychology from Brown University, demonstrating her expertise in applying psychological principles to industrial efficiency and management. Her dissertation was titled “The Psychology of Management.”

Frank Gilbreth's sudden death left Lillian a widow with eleven surviving children (one died in childhood). Despite the personal tragedy, Lillian persevered and continued their work, eventually surpassing him in influence in the field.

After Frank's death, Lillian focused on consulting, teaching, and writing. She consulted for various companies, worked on home economics projects, and taught at Purdue University, becoming a full professor in 1948. She was a pioneer for women in engineering.

Lillian made significant contributions to kitchen design, focusing on ergonomics and efficiency to improve the lives of homemakers. She designed the 'work triangle' concept, which optimizes the placement of the sink, stove, and refrigerator to minimize unnecessary movement.

During World War II, Lillian consulted for the U.S. government, applying her expertise in efficiency to improve productivity in war-related industries.