Quinn first appeared as muscle for James Sterling in The First David Job. He was sent to take on hitter Eliot Spencer, and actually achieved a victory. This victory was only momentary because Eliot eventually knocked Quinn unconscious.
Eliot reminds Quinn that he was unconscious for the end of their last fight in "The Last Dam Job." However, Sterling's scheme was (somewhat) foiled by the Leverage team. Unlike Alec Hardison's personal rivalry with his counterpart Colin "Chaos" Mason, Quinn and Eliot have a very professional relationship and respect one another's work, but their recent bosses have conflicts and by default, they are presented as enemies.
He reappeared in The Last Dam Job, being hired as Eliot's replacement for the con. Eliot himself hired him, having to help rescue him from a dangerous capture scenario. Quinn and Eliot shared a mistrust of hackers such as Alec Hardison and Colin "Chaos" Mason. While Eliot and Hardison tried to sabotage one dam, Quinn and "Chaos" successfully sabotaged the other.
Quinn and Eliot played nearly identical roles in the final showdown.