In a large pot, heat the olive oil over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.

Add the minced garlic, diced carrots, and celery. Cook for another 5 minutes, stirring occasionally.

Stir in the chopped Swiss chard and cook until wilted, about 3 minutes.

Pour in the vegetable broth, add thyme, bay leaf, salt, and pepper. Bring to a boil, then reduce heat and simmer for 20 minutes.

Remove the bay leaf. For a smoother texture, blend the soup with an immersion blender or in batches using a regular blender.

Adjust seasoning if necessary and serve hot.