The 27-year-old striker becomes the ninth new arrival at Meadow Lane this summer as the Magpies continue to flex their financial muscle in League Two following the takeover by middle east consortium Munto Finance.
"Karl is a player we have had on our shortlist for most of the summer," said McParland. "He wasn't available when we enquired about him a few weeks ago but since then things have changed at Preston and we learned last week we might be able to get him.
"Karl has been prolific at this level and also higher up the football pyramid, so I am really pleased to have him on board."
Hawley, who scored 26 goals during Carlisle's promotion-winning League Two campaign in 2005/06, began his career with Walsall and had loan spells at Raith and Hereford before joining the Cumbrians in 2004.
He scored 51 goals in 137 appearances for the Brunton Park club before following his old manager Paul Simpson to Preston in 2007.