This hearty slow cooker lentil soup is filled with vegetables and packed with plant-based protein. This cozy soup is healthy comfort food at its finest and it’s so simple to make!

lentil soup
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We eat a lot of lentil soup and after years of making my stovetop lentil soup, I shared an Instant Pot Lentil Soup that can be made quickly! But then I started thinking, why not share a slow cooker version, too? It’s a great one to make before work so you can come home to delicious soup. This soup is surprisingly hands off. Just add everything to the slow cooker and turn the dial to start. It really is that easy!

Why I Love Lentils

As a vegetarian, I love lentils because they’re a great source of plant-based protein! They’re also an excellent source of fiber which means this soup will really fill you up. They add a heartiness to this meal, but lentils are very inexpensive, so it’s a great budget-friendly alternative to something like beef. Plus, lentils last a long time in the pantry so you can always keep some on hand without worrying about a looming expiration date. If you’re looking for another way to use them, try my Southwestern Lentil Soup!

Health Benefits of Lentils

As I mentioned, lentils are an excellent source of plant-based protein. They contain 9 grams of protein per 1⁄2-cup serving. They also contain fiber as well as vitamins and minerals. They’re one of the cheapest protein sources you’ll find at the grocery store. If you love lentils as much as I do, try my simple spiced lentils.

lentil soup ingredients

Ingredients and Substitutions

  • Mirepoix– The onion, carrot, and celery are a traditional mirepoix base. If you’re missing an ingredient, check out this post for substitution options.
  • Lentils– You’ll need brown or green lentils for this recipe. Red lentils and black lentils cook differently and can’t be used in this recipe.
  • Garlic powder– Normally I recommend fresh garlic for soups, but since we’re skipping the sauté I actually prefer garlic powder in this recipe.
  • Bay leaf– A bay leaf adds a savory, slightly citrusy flavor. You can leave it out if you don’t have any.
  • Cumin– This adds additional flavor with a hint of earthy spice.
  • Thyme– Dried thyme adds a savory flavor. Substitute with 1/4 teaspoon dried rosemary if you don’t have any dried thyme.
  • Vegetable Broth– I like Edward & Son’s “Not-Chicken” style broth, but any style broth is fine.
  • Lemon juice– A like adding a squeeze of lemon juice at the end to brighten the flavors of the soup. You could also do this with a little vinegar.

Optional Additions

I have a few variations of this lentil soup, so feel free to play around with this recipe! You can add a can of diced tomatoes to add an additional layer of flavor and boost the vegetables in this soup. You can also add fresh spinach or kale at the end. Simply add in a few handfuls of chopped greens (be sure to remove kale stems) and stir. Let it cook for a few minutes until the greens are bright in color. This soup is also delicious with a sprinkle of fresh Parmesan cheese for additional savory flavor. As always, be sure to season your soup with salt and pepper to taste.

lentil soup

What size slow cooker do I need?

I used this large 8 quart oval-style Crockpot brand slow cooker, but any brand of slow cooker should work fine for this recipe. You’ll need at least 6-quart capacity to avoid overflowing and to ensure that the soup can cook evenly. It’s also the perfect size for my vegan slow cooker chili!

How to Make Lentil Soup in a Slow Cooker