Start by rinsing your pearl barley under cold water until the water runs clear, then set aside. Prepare your vegetables: peel and roughly chop the carrots, dice the onion, and mince the garlic. Pat the chicken thighs dry and set aside.
Place the chicken thighs into the slow cooker, spreading them out evenly. Add the chopped carrots, diced onion, minced garlic, and dried thyme over the chicken. Pour in the chicken broth, making sure the ingredients are mostly submerged.
Cover the slow cooker with its lid and set it to cook on low for 6 to 8 hours, or on high for 3 to 4 hours. During this time, the chicken will become tender and flavorful, and the vegetables will soften.
About an hour before the cooking time ends, open the lid and add the rinsed pearl barley to the slow cooker. Stir gently with a wooden spoon, making sure the barley is submerged in the broth. Cover again and continue to cook until the barley is plump and chewy, about an hour.
Once the cooking time is up, carefully remove the chicken thighs from the slow cooker. Shred the meat with a fork, discarding any bones or excess fat. Return the shredded chicken to the pot and stir well to combine all the flavors.
Taste the soup and season with salt, pepper, and a squeeze of fresh lemon juice to brighten the flavors. Stir everything together and let it rest off the heat for 5 minutes.
Serve your hearty chicken barley soup hot in bowls, garnished with a sprig of fresh herbs if desired. The broth should be thick and flavorful, with tender chicken and chewy barley creating a comforting texture.
