The decision came from Stuart Lancaster after Quins flanker Chris Robshaw cracked a bone in his thumb in Saturday's 36-27 defeat, ruling him out of the remainder of the tour.
Hartley, who has captained his club since 2009, becomes the second Saint to skipper England this summer after Phil Dowson did so against the Barbarians last month. Lancaster believes the hooker will make a seemless transition into the role.
"Dylan Hartley will captain the side," he revealed earlier today. "He has been a key part of our leadership group and I know he will step up to the task on Saturday."
The team for Saturday's Test, which kicks off at 4pm BST, is due to be confirmed on Thursday.