[1] He was previously director of the Information and Communications Laboratory at the Georgia Tech Research Institute and is a retired officer of the United States Navy Reserve.

[9] On July 9, 2004, when McGarrah was a rear admiral, the Secretary of the Navy, Gordon R. England, appointed him the Director of the Office for the Administrative Review of the Detention of Enemy Combatants (OARDEC).

[10][11] McGarrah testified before the Senate Judiciary Committee about the Combatant Status Review Tribunals (CSRT), held in the Guantanamo Bay detainment camps, in Cuba, from July 2004 to March 2005.

[12][13][14] McGarrah testified that, to take into account the concerns of United States Supreme Court rulings the CSRT were modelled after Army Regulations 190-8 (Enemy Prisoners of War, Retained Personnel, Civilian Internees and Other Detainees), subchapter 1–6, Tribunals.

[6] McGarrah came to the Georgia Tech Research Institute in November 2008, taking the position of director of the Information Technology and Telecommunications Laboratory (ITTL).