Gallen joined Luton after leaving MK Dons last summer
Luton Town moved to within a point of second-placed Oxford with their fourth consecutive Blue Square Premier win.
The Hatters opened the scoring when Scott Howells fired home a half-volley from outside the area and Kevin Gallen soon doubled their lead from 18 yards.
Harriers were quick to respond with James Lawrie reducing the arrears before the break with a left-footed shot from the edge of the area.
But Gallen sealed Luton's win with an impressive finish from inside the box.
Gallen's experience proved to be the difference as the veteran former Queens Park Rangers striker produced two high-class finishes to secure the Hatters' victory.
The 34-year-old finished off a set-piece for his first, firing Simon Heslop's short lay-off past Harriers keeper Ross Atkins, who could only get a hand to the ball.
And Gallen showed his striker's instinct with his second, bursting through the Harriers defence to fire home from an acute angle.
Harriers' response was to push Luton back immediately but Lee Baker and Jack Byrne failed to find the net as Steve Burr suffered his first league defeat as manager.
Robbie Matthews also went close for Kidderminster but his direct free-kick was well saved by Luton keeper Mark Tyler and he headed wide from close range late on.
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