The 17-year-old, who made nine appearances for the League One side, follows Jonathan Leko back to the Baggies after the 18-year-old winger was recalled from Bristol City.
Pardew is looking at Harper and Leko this month in a bid to bolster the options in his squad.
Both teenagers were handed their senior Albion debuts by former boss Tony Pulis.
Exeter City want to keep 17-year-old right-back Kane Wilson and 19-year-old midfielder Kyle Edwards for the remainder of the season.
Both of their loan deals expire this week, but Wilson scored his first senior goal for the Grecians at the weekend and talks are underway to extend the loans until May.
However, neither Wilson nor Edwards will be available for Exeter in their FA Cup third round clash with the Baggies this coming Saturday.
Defenders Shaun Donnellan and Jack Fitzwater – who scored on New Year's Day for Forest Green Rovers – have returned from their six-month loans.
Tyler Roberts, who has scored five goals for Walsall this season, is on loan at the League One club until January 27, but a number of clubs are circling the 18-year-old, whose contract runs out in the summer.
Albion have already rejected a multimillion bid for the teenager, and have offered him a new deal.