Dice the chicken thighs into bite-sized pieces and chop the onion. Slice the carrots into thin rounds. Rinse the barley thoroughly under cold water and set aside.
Add the diced chicken to the bottom of the crockpot, spreading it out evenly.
Pour the sliced carrots and chopped onion over the chicken, distributing them evenly across the surface.
Sprinkle the rinsed barley over the vegetables, ensuring an even layer.
Pour the chicken broth over all the ingredients, making sure everything is submerged. Tuck in a sprig of fresh thyme or sprinkle dried thyme on top.
Cover the crockpot with the lid and set it to low. Let it simmer for 6 to 8 hours, until the chicken is cooked through and easily shreds, and the barley is tender and plump.
About 30 minutes before serving, open the lid and taste the broth. Adjust seasoning with salt and pepper as needed, then stir gently to combine all flavors.
Once ready, serve the soup hot, garnished with fresh herbs if desired, and enjoy the comforting aroma and hearty texture.