He serves as chairman of the Credentials Committee at Saint Francis Hospital, and is currently the president of the Warren Cancer Research Foundation. Previously he held the positions of Chief of Staff and Chief of Surgery. 

Dr. Lockhart was raised in Jackson, Mississippi. He graduated from Millsaps College and earned his medical degree from the University of Mississippi in Jackson. 

Dr. Lockhart has played an important role in cancer research and the care of patients with cancer. As chairman of the Cancer Committee at Saint Francis, he helped outline the hospital’s commitment to comprehensive cancer care. Since 1976, he has served as cancer liaison representative of the American College of Surgeons Committee on Cancer, and was previously State Chairman of the College of Surgeons Cancer Liaison Program.

He is a member of both the Surgery Committee and the Melanoma Committee of the Eastern Cooperative Oncology Group, and was co-principal investigator for the National Surgical Adjuvant Breast Project's first Breast Cancer Prevention Trial, and now is principal investigator for the second Breast Cancer Prevention Trial, and a member of the Breast Committee for that organization. He has also served on both the Board of Directors and the Professional Education Committee of the American Cancer Society in Oklahoma. In 1992, he acted as visiting surgeon at the M.D. Anderson Cancer Center in Houston. He is currently the Governor for the Oklahoma State chapter of the American College of Surgeons.

Since 1988, Dr. Lockhart has been the Vice Councilor for Oklahoma of the Southwestern Surgical Congress. He is a Fellow of the American College of  Surgeons and a member of the American Medical Association, Oklahoma State Medical Association, Tulsa County Medical Society, Oklahoma Surgical Society, Tulsa Surgical Society, The American College of Physician Executives, Society for Surgery of Alimentary Tract, Society for the Study of Breast Diseases, American Society of Clinical Oncology, Collegium Internationale Chirurgiae Digestivae, and Parkland Surgical Society. He holds the position of Clinical Professor of Surgery at the University of Oklahoma College of Medicine in Tulsa.