UMass Memorial Health Care said Wednesday that it has hired Dr. Eric W. Dickson as president and chief executive, replacing John O’Brien, who is retiring from the helm of the largest health care system in Central Massachusetts.

The appointment takes effect­ Feb. 25.

Dickson, 46, has been serving as president of UMass Memorial­ Medical Group, a 1,060-physician subsidiary of the Worcester-based health care system, and senior associate dean at the University of Massachusetts Medical School, which is affiliated with its hospitals.

He graduated from Merrimack College, the University of Massachusetts Medical School, and Harvard University School of Public Health.