Lewis B. Stillwell transferred to Lehigh University from Wesleyan University in 1884 to study electrical engineering. He was an editor of the Epitome yearbook, and a member of Alpha Delta Phi. Immediately following his 1885 Lehigh graduation, he began his career at the Westinghouse Company in Pittsburgh, PA. The company focused on power engineering. During Stillwell's tenure at Westinghouse, the company completed some of the most important power projects of that time.
In 1895 Stillwell wrote a paper that would eventually jump start his career. The paper was titled "Electric Power Generation at Niagra" and was published in a respected technical periodical. Just one year later, the Niagra power plant introduced what became known as the "Stillwell regulator," a mechanism that employed power transformers with multiple taps in order to stop the power plant from producing more power than was needed.
In 1897 Stillwell left Westinghouse to become the electrical director of the Niagra Falls Power Company, a position he held until 1900 when he left the company and established his own consulting practice. His clients included the Manhattan Elevated Railway Company, the Rapid Transit Subway Construction Company, and the New York, New Haven and Hartford Railroad. He also consulted on the Holland Tunnel and for the New York Port Authority.
In 1933, Stillwell was awarded with the Lamme Medal, established by the AIEE, of which he was president for many years. The medal recognized his "distinguished career in connection with the design, installation and operation of electrical machinery and equipment."