Gather all ingredients.

Whisk together pickle juice, brown sugar, kosher salt, 1 teaspoon black pepper, and 1 pinch cayenne pepper in a large bowl until sugar dissolves. Place chicken breasts in brine, using a plate or bowl to keep breasts submerged. Refrigerate for 1 to 2 hours.

Preheat an outdoor grill for medium-high heat and lightly oil the grate.

Remove chicken breasts from brine, discard brine, and dry chicken breasts with paper towels. Brush each breast with olive oil; season with salt, black pepper, and cayenne pepper. Cook chicken on the preheated grill until no longer pink in the center and the juices run clear, about 5 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).

Transfer chicken to a plate, tent with aluminum foil, and let chicken rest for 5 minutes.