Mix sugar and water together in a medium saucepan. Add the whole strawberries and bring to a low simmer. Cook for 10 minutes without stirring.
Strain into a bowl or jar using a spoon to mash the strawberries as they strain. Skim off any bubbles. Store in an airtight container in the fridge.
Sangria
Add orange and strawberry slices to a 2.5-quart pitcher.
Pour in orange juice, cranberry juice, lime juice, wine, vodka, and 1/2 cup strawberry simple syrup. (You can add more or less strawberry syrup to taste.) Stir to combine.
Chill in the fridge for 2 hours to overnight.
Pour into glasses, being sure to add some fruit to each glass.