Combine soy sauce and garlic in a large, nonporous bowl. Add chicken and turn to coat. Cover and marinate in the refrigerator for at least 1 hour.
Preheat an outdoor grill for medium-high heat and lightly oil the grate.
Cook chicken on the preheated grill until no longer pink in the center and the juices run clear, 10 to 15 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Discard marinade.