From May 1974 to May 1993 he held various administrative positions within the Texas Department of Mental Health and Mental Retardation, including work in the areas of personnel, fiscal services and hospital support. He was superintendent of the Terrell State Hospital and Deputy Commissioner for Mental Health Services for the state of Texas.  He served three years as head of the Dallas County Board of Mental Health and Mental Retardation's service system for people with disabilities.
 

From 1995-98 he headed the state mental health and mental retardation system, and in 1998 was appointed by Gov. George W. Bush and confirmed by the Texas Senate to lead the state's health and human services agencies as commissioner of health and human services. His responsibilities include oversight of 13 separate health and human services agencies, with total spending of $14 billion per year and 54,000 employees. 

Gilbert is a member of the American Public Human Services Association, member of the board of directors of the National Association of State Mental Health Program Directors, on the board of governors representing Region VI, and a certified board examiner of the Association of Behavioral Healthcare Management, member of the American College of Health Care           Executives, and adjunct associate professor of the Department of Psychiatry, Southwestern Medical School, University of Texas Health Science Center in Dallas. 

Gilbert has authored several articles in such professional publications as Journal on Quality Improvement, AMHA Leader, The Journal of Mental Health Administration, Community Support Network News, The Journal of Clinical Psychiatry, and a book chapter on state hospital reform.