After earning a B.S. in chemistry at Houston-Tillotson College in Austin, Texas, Harris served in the army. Later, he joined Tracerlab, Inc. in Richmond, California, where he worked as a chemist for five years. In 1960, Harris left Tracerlab to accept a position in the Nuclear Chemistry Division of the Lawrence Radiation Laboratory at the University of California, Berkeley. He became part of the team that discovered and identified elements 104 and 105 in 1969-1970. His job was to create the targets used in the identification of elements 104 and 105. In a press release at the time, his colleague Albert Ghiorso stated that James Harris created "the best target that has ever been available for heavy-element research".
In a 1973 interview with Harris, Jack Slater from Ebony magazine wrote:
If Harris were to write the book [on his job-hunting experiences and the problems a black scientist encounters], it might include the half-dozen or so shocked expressions of prospective employers when he first walked into their offices. It might also include the half-dozen secretaries who refused to believe he was applying for job as a chemist rather than a janitor. "At one point," he recalls, chuckling now at an old wound. "I was even given a job test simple enough for elementary school kids--basic addition and subtraction...I told the secretary I didn't need a job that badly." (p 148)In 1973, Harris received an honorary Ph.D. from Houston-Tillotson College and later the Scientific Merit Award from the Mayor of Richmond, California. Also honored by the National Urban League with a Merit Award, he has been invited to lecture at numerous colleges and universities. In addition to a busy professional life, Harris and his wife Helen have five children.