Cline returned to Oklahoma to accept the position of Commissioner of the Oklahoma Department of Mental Health and Substance Abuse Services during the administration of Republican Governor Frank Keating. He began that role in January 2001. As Commissioner, Cline was responsible for providing public health services relating to mental illness and substance abuse.
Henry Administration
Democratic Governor of Oklahoma Brad Henry appointed Cline as Secretary of Health in 2004 following the resignation of Tom Adelson to run for the Oklahoma Senate. Cline continued to serve concurrently as Commissioner in addition to his duties as Health Secretary. As Secretary, Cline served as Governor Henry's chief health policy advisor and had supervision over the Oklahoma State Department of Health and the Oklahoma Tobacco Settlement Endowment Trust.
SAMSHA Administrator
nominated Cline to serve as the Administrator of the Substance Abuse and Mental Health Services Administration, an agency of the United States Department of Health and Human Services, in November 2006, and his nomination was confirmed by the U.S. Senate in December. At the end of August 2008, Terry Cline became the HHS Department’s Health Attaché and representative at the U.S. Embassy in Baghdad, Iraq. As Health Attaché, Cline coordinated HHS programs in Iraq and provided advice to the U.S. ambassador, HHS Secretary and others. He also was a liaison to Iraq’s Ministries of Health, Higher Education and Social Affairs, and worked with international organizations, private partners and other U.S. government agencies engaged in health-related activities in Iraq.
State Health Commissioner
In June 2009 Cline became the Commissioner of the Oklahoma State Department of Health. He replaced Michael Crutcher who had retired the previous January.
Fallin Administration
On February 1, 2011, Republican Governor of Oklahoma Mary Fallin announced she had selected Commissioner Cline to serve as the Oklahoma Secretary of Health and Human Services in her Cabinet. As Health and Human Services Secretary, Cline had oversight over all public health and public assistance agencies of the State government. Cline continued to serve as Health Commissioner in addition to his duties as a Cabinet Secretary.
Resignation
On October 30, 2017, Cline submitted his resignation to the State Board of Health, during an emergency meeting of the Board. The Board named Preston Doerflinger as the Interim Commissioner of Health during the meeting. Cline's resignation was prompted by allegations of financial mismanagement within the Department, which were subsequently investigated by the Oklahoma State Auditor.