Let the cream cheese sit at room temperature for 30–60 minutes so it becomes easy to mix. Softened cream cheese creates a much smoother dip.
Add the cream cheese and mayonnaise to a large mixing bowl. Beat with a hand mixer until smooth and creamy, with no visible lumps.
Mix in the garlic powder and black pepper. Stir until the seasonings are evenly distributed throughout the creamy base.
Fold in the chopped green olives and shredded cheddar cheese. Mix gently until everything is evenly incorporated while keeping some small pieces of olive visible for texture.
Stir in 1 tablespoon of reserved olive brine. Taste the dip and add another teaspoon or two if you want a stronger olive flavor or slightly softer consistency. Adding the brine gradually helps control the saltiness.
Cover the bowl and refrigerate for at least 1 hour. For the best flavor, make the dip several hours ahead or the day before serving. Chilling allows the garlic and olive flavors to mellow and blend together.
Transfer the chilled dip to a serving bowl and garnish with a few whole olives and fresh parsley, if desired. Serve with crackers, potato chips, crostini, or fresh vegetables.
