Brown the ground venison with the onion, garlic, salt and pepper in a skillet, stirring until venison is crumbly; drain.
Cook the potato for 5 minutes in boiling water; drain.
Layer the potato, venison mixture, mushrooms and vegetables in a pastry-lined pie plate.
Spread the cream of mushroom soup evenly over the vegetables to within 2 inches of edge of plate.
Top with the remaining pastry, sealing edge and cutting vents.
Preheat the oven to 425 degrees.
Cover the edges of the pastry with strips of foil.
Bake for 15 minutes.
Reduce oven heat to 375 degrees.
Bake for 45 minutes or until golden brown and bubbling through the vents, removing the foil strips for the last 10 minutes of baking.
Let stand for 5 minutes before serving.