She was educated at Goucher College in Maryland and Columbia University in New York City. She taught math in the Baltimore City schools for ten years. She then proceeded to earn a degree in civil engineering at Cornell University. In the year 1920, this in itself was a remarkable achievement, as few women had access to a college education. Olive Dennis was more than remarkable; she is a legendary B&O employee.
She began her career as a draftsman, helping to design bridges. She was soon elevated to the position of Engineer of Service, focusing on improvements in passenger service. She was responsible for the development of a new ventilation system, improved lighting, and more comfortable seats. She also helped design a state of the art luxury passenger train that whisked passengers between Baltimore and Cincinnati. She was a true pioneer.