Garvey is a Breton and Expert-level Sneak trainer. He is kind of the leader of the Warrens.
Garvey is generally found standing at the entrance in The Warrens, a series of tunnels underneath Markarth where the poor and impoverished sleep.
On the Dragonborn's hunt for information on the Forsworn agent, Weylin, Garvey can be persuaded, intimidated, or paid to relinquish the key to Weylin's room.
If questioned about Weylin himself, Garvey seems less concerned about Weylin's murderous deed than who will occupy the Reach native's room next.