After receiving the proper credentials, Turner headed to the Tuskegee Institute, Alabama, where he served as teacher of biology. He later taught at various public schools in Baltimore, Maryland. From 1914 to 1924, he served as Professor of Botany at Howard University and also served from 1914 to 1920 as the Acting Dean at the Howard's School of Education.
While working at Cornell University in 1918, did special work for the U.S. Department of Agriculture in Maine, where he examined potato fields. The American government consulted Turner throughout his career about agricultural problems. Under the auspices of the United States Secretary of Agriculture, Turner worked as a collaborator on Virginia's plant diseases. He was laso the first black person ever to receive a doctorate from Cornell. In 1931, Turner organized the Virginia Conference of College Science Teachers in 1931, and served as president of that group for two terms. Turner also was a member of the American Association for the Advancement of Science and of the American Society of Horticultural Science, both of which he was very active in.
Turner was also known as an activist who was a staunch defender of black rights and civil liberties. His activism, curiously, has overshadowed his many scientific accomplishments. In 1909, he was a founding member of the of the National Association for the Advancement of Colored People (NAACP), and was also active in trying to get blacks the right to vote. He was eventually honored with a lifetime membership in the NAACP.
Dr. Turner was active in Catholic organizations and in societies for the advancement of the African-American. In 1925, Turner founded the Federated Colored Catholics (FCC), an organization that he said was "composed of catholic Negroes who placed their services at the disposal of the Church for whatever good they were able to effect in the solution of the problems facing the group in Church and country". Turner remained a loyal member of the Catholic Church. In 1976, Washington, D.C.'s Black Catholics named its highest award for Turner. That same year at age 99, Turner was awarded a degree by the Catholic University of America.
He died at the age of 101 in 1978, 36 days after celebrating his birthday.