Gather all your ingredients and chop the onion and celery into small, even pieces. Mince the garlic and set everything aside.
Heat olive oil in a heavy-bottomed pot over medium heat until shimmering. Add the chopped onion and cook, stirring occasionally, until it becomes translucent and fragrant, about 5 minutes.
Place the chicken thighs into the pot, season with salt and pepper, and sear until browned on both sides, about 8 minutes. This creates a flavorful crust and releases delicious juices.
Pour in the chicken broth, then add the diced celery, minced garlic, and a teaspoon of dried thyme if using. Bring the mixture to a gentle simmer.
Reduce the heat to low and cover the pot. Let the soup simmer gently for about 30 minutes, allowing the chicken to become tender and flavors to meld. Skim off any foam or fat that rises to the surface.
Remove the chicken thighs from the soup and shred the meat into bite-sized pieces. Return the shredded chicken to the pot and stir well.
Taste the soup and adjust the seasoning with salt and pepper as needed. Add a splash of freshly squeezed lemon juice to brighten the flavors.
Let the soup rest for a couple of minutes so the flavors can meld further. Then, ladle the hot soup into bowls.
Garnish each bowl with chopped fresh parsley for a pop of color and freshness.
Serve hot and enjoy your cozy, nourishing keto chicken soup with a slice of crusty bread or a simple side salad if desired.