Kennard was born in Columbus, Ohio and studied at Pomona College and Oxford University as part of a Rhodes Scholarship. He went on to earn his Ph.D. from Cornell in 1913, where he would continue most of his scientific career. During a 1926 sabbatical spent at the University of Göttingen, he learned the newly developing quantum mechanics of Werner Heisenberg and Pascual Jordan. With this knowledge, he derived the first rigorous form of the uncertainty principle and fully solved several simple quantum mechanics problems for the first time. In 1926, he was appointed professor of physics at Cornell, which he remained until 1946.