During his summer breaks from school, he interned at Bell Laboratories, and eventually was hired as one of the first African Americans at the company. James was asked to solve a problem: in order to discover more about how humans hear, researchers needed a powerful microphone that could detect small noises. In the 1960s, such a thing didn't exist. James and his teammate Gerhard Sessler had two challenges: making a better microphone that could convert sound to an electrical signal, and making the microphone work without a big battery. After years of research, they developed a specific combination of plastic and metals, that when combined into a very small film, created a powerful microphone the size of a shirt button, that didn’t need a big battery – it stayed charged for a long time by itself! Not only that, the new invention was cheaper than any other microphone.

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Still today, the technology that James and his team invented can be found in 90% of microphones, and is used in phones, hearing aids, and recording equipment for musicians. James was inducted into the National Inventors Hall of Fame in 1999. In 2001,he retired from Bell Labs after 40 years, and became a professor at John Hopkins University. He teaches, conducts his research, and is active as a mentor and advocate for minorities and female students who are interested in entering STEM fields.

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