Dr. Mannion was raised in Pennsylvania, attended the Massachusetts Institute of Technology (MIT), where he majored in chemical engineering. He then continued with parallel clinical and research training at the New York University School of Medicine, simultaneously receiving an MD and a PhD.
He completed an internship and residency in internal medicine at Brigham & Women's Hospital and a fellowship in medical oncology at Dana Farber Cancer Institute both in Boston.
Dr. Mannion has been practicing medical oncology full time in Cincinnati for over 20 years. He provides care for all types of malignancies but has a special interest in genitourinary cancers which include cancers of the prostate, bladder, testicles, and kidneys. He was one of the founders of the Prostate Cancer Collaborative at Christ Hospital, a multidisciplinary program where patients are seen simultaneously by several prostate cancer specialists to optimize their care.
Dr. Mannion also has an interest in hospital administration. He serves as the medical director of oncology services at The Christ Hospital Health Network, overseeing operations of the oncology service line. He also sits on various hospital committees at the administrative level.