Chop onion into large chunks and place in the bottom of a 6-quart crock pot.
Top with corned beef and seasoning packet.
Pour water into the crock pot until it just about covers the corned beef.
Add garlic, bay leaves, salt and pepper.
Cook on low 8 - 10 hours.
After the initial 3 hours, add potatoes, carrots and cabbage to the crock pot.
Remove corned beef from crock pot and let rest 15 minutes before slicing.
Serve with potatoes, carrots and cabbage.