In a mixing bowl or sealable jar, combine the olive oil, lemon juice, minced garlic, lemon zest, chopped thyme and rosemary, salt, and black pepper. Whisk thoroughly until the marinade is well emulsified.
Arrange the chicken thighs in a shallow container or resealable plastic bag. Pour most of the prepared marinade over the chicken, setting aside a small portion to use during grilling. Ensure the chicken is evenly coated, then cover or seal and refrigerate for a minimum of 30 minutes and no longer than 2 hours to avoid over-marinating.
Preheat a grill or grill pan over medium heat. Lightly oil the grates to prevent sticking. Remove the chicken from the marinade, allowing excess to drip off, and discard the used marinade.
Grill the chicken for 5 to 6 minutes per side, or until fully cooked and the internal temperature reaches 165°F. During the final moments of grilling, brush the reserved marinade over the chicken for enhanced flavor.
Once grilled, transfer the chicken to a plate and allow it to rest for 5 minutes before serving.