Pat Walsh is a contractor with the CIA.
In our initial introduction to him, he is a colonel in the U.S. Army, recently attached to "the Army Special Operations Cell within the Army's G3 shop" at the Pentagon. That sounds impressive but he would be the first to admit that it amounted to being "placed in a small windowless office with the other 'slide monkeys'", a not so impressive term used for those just toiling away for the Army Chief of Staff. Prior to that recent transfer, Walsh had been stationed in Iraq.
Walsh's experience in the military is extensive and is reflected in the medals he wears, most notably the "Purple Heart with three oak leaf clusters, Bronze Star with V device and four oak leaf clusters, Silver Star with oak leaf cluster and Distinguished Service Cross". These show clearly that his time in combat was not spent behind a desk so being put behind one as we find him will chafe a bit.
Unfortunately for him, he will be forced to make a change he was not expecting. As we are told in a blurb for the first recorded tale, "he screws up and picks the wrong side of a political battle. When an old Army buddy recruits Pat to work as an asset for the CIA, he reluctantly agrees, and the adventure begins."
Between the bureaucratic fiasco that causes Walsh to have to leave the military and his decision to help out the Agency, Walsh, who is married with four children, tried his hand at the home construction business and was starting to do quite well when the sub-prime scandal hit the financial world and his bank played very dirty with him. His personal finances in turmoil and two of his older children in college, a huge drain in his income, Walsh decides to take a temporary job over in Afghanistan.
It will be there that he is approached to help out the Agency while still working his paying job there. Walsh is not an agent, per se, working, at least at first, as a contractor but that just seems to mean that when things go bad, he and those working with him, are really on their own.