[4] Donahue graduated from Pennsylvania's Chambersburg Area Senior High School in 1987, and then attended Wyoming Seminary.

In 2002 Donahue volunteered for and completed a specialized selection and operator training course for assignment to the army's 1st Special Forces Operational Detachment – Delta, publicly known as Delta Force, at Fort Bragg, North Carolina.

[13][14] The nomination was placed on hold due to senatorial questions regarding his handling of the withdrawal of U.S. forces from Afghanistan in 2021.

[17] On the morning of 11 September 2001, Donahue, who was a captain at that time, was on Capitol Hill accompanying Vice Chairman of the Joint Chiefs of Staff General Richard Myers, to whom he was an aide.

[20][19][18] At one point Donahue also lent his cell phone to Myers who used it to call General Ralph Eberhart, the Commander-in-Chief of the North American Aerospace Defense Command, to get further information regarding the situation.

[18][20][19] Myers was designated as Acting-Chairman of the Joint Chiefs of Staff at the time of the attack, because Chairman General Hugh Shelton was en route to Europe for an upcoming NATO summit, and Donahue remained with him throughout the day.