MacReady entered the army as soon as he was able and, when he turned 25, he joined the United Kingdom Special Forces. 4 years later, he was recruited into the Special Reconnaissance Regiment, where he would end up spending 12 years hunting down terrorists among every desert on the planet. However, near the end of those 12 years, he became disgruntled and quit when he realized that no matter how many terrorists they took out, more kept popping up. An unknown time later though, he returned to hunting down terrorists for TF29, feeling it was his purpose in life and to keep his skills sharp.
Of all the members of Task Force 29, Duncan MacReady is the longest serving member behind Director Jim Miller and one of its top agents. As he is the senior agent, and in charge of TF29's armed operations, he takes his orders directly from Miller and passes them along to his team. However, as Adam Jensen is on his team and is the only augmented field agent, Miller will bypass the chain of command and directly issue orders to Jensen himself, which does not sit well with MacReady.
To most people, MacReady usually comes off as rude, with no patience for incompetent people. He is aware of his insensitivity and will sometimes try to mitigate it, as shown in his conversation with Jensen in his office. He rarely shows approval, but if one did an exceptional job, he will say so.
He distrusts augmented people, and is therefore wary of Jensen when he joins his TF29 team. If pressed by Adam, he reveals that part of the reason he distrusts Augs is because he lost 3 of his team members when the Aug Incident happened. This discrimination is well known among other TF29 agents as well, with various agents commenting about it and Miller even asking him to keep an open mind about Aria Argento, the only other TF29 Aug.
Despite MacReady's distrust in Augs, he does value their skills and contribution, as he willingly recommended Aria Argento for his team once she was cleared for the field, even remarking that she shoots better than anyone on his team.
- For some reason, Mac's Infolink icon displays him in civilian clothing instead of the combat gear he would wear while on a mission during the finale in London.
- His surname is displayed as "Macready" in the subtitles with an uncapitalized "r" instead of "MacReady".