Put the garlic, olive oil, Dijon mustard, honey, salt, black pepper and rosemary in a zip-top bag. Seal the bag and squeeze it gently to combine the marinade.
Add the chicken, seal the bag and turn it until the thighs are coated. Refrigerate for at least 1 hour or up to 24 hours.
Preheat the grill to medium-high heat, about 350 to 400°F (180 to 200°C).
Remove the chicken from the bag and discard the used marinade.
Grill with the lid closed for about 6 minutes per side. Check the thickest part with a meat thermometer and continue cooking until it reaches at least 165°F (74°C).
Transfer the chicken to aluminum foil and squeeze the lemon juice over it. Fold the foil loosely around the chicken.
Rest for 10 minutes, then serve.