John Dennis O'Connor (born 1942) is an American biologist and was the sixteenth chancellor (1991–1995) of the University of Pittsburgh.
At the University of North Carolina, he was vice chancellor of research and graduate studies and dean of the graduate school before being appointed vice chancellor of academic affairs, and provost in 1988.
In 2002 the University of Maryland, College Park named him vice president for research and dean of the graduate school.
He resigned this post effective July 1, 2004, and assumed the position of professor in the Department of Biology.
According to the Diamondback, the University of Maryland newspaper, O'Connor was deemed responsible for overallocating graduate student fellowships, an error creating a domino effect that has left the graduate school in a multimillion-dollar deficit.