What is the best exercise for chronic low back pain?

I find that exercise in general helps a lot, especially heavy weights. My back pain disappeared once I hit a heavy, mass-building routine. Work your legs. Work your core. Strengthen your back. Work on your posture. Use stretches and yoga postures.
Another thing to consider, which has made a world of difference to me, is your mattress. Get a good memory-foam mattress and your back pain will fade away.

Deadlifts will strengthen the muscles of the lower back like no other. I do, however, recommend that you consult a physical therapist so that they can diagnose the cause of your pain and help you map a way forward.

Butterfly stretch – lay on a mat with your knees together and feet flat on the floor. Slowly bring your knees outwards and let gravity do the rest. Try to relax into the stretch, taking deep breaths. Hold for 1 minute (or 30 secs minimum).

Strengthening your core can really help with lower back pain. Consider pilates or yoga (watch on YouTube if on a budget), and most importantly keep moving! Being less active because of joint pain etc. can end up causing you more pain.

An awesome exercise is stretching your whole back. Do not do extreme workouts, for this will irritate your back more. You may do the cobra, child pose, as well as other yoga stretches. Hope this helps.

I like partial crunches and core strengthening exercises, combined with stretching. For me, the cat/cow combination feels really good! I don't think there is any one best exercise for everyone across the board; it depends on the nature, frequency, and intensity of your particular low back pain. Try different things and see what works for you, and as always, seek the advice of a qualified physician or physical therapist that you trust.

Back preassure release through wall stretch https://youtu.be/5w5SBM05g7s
I also suggest to visit a good osteopathy specialist.

Yoga is super great for back pain. I highly recommend Yoga with Adrienne, which is a YouTube channel with tons of free yoga. She has stuff for all levels of experience and is super positive and fun too!

Specific stretch positions and hot showers help me. If it's a serious chronic back problem or injury I would suggest actually looking for a professional or getting a back brace.

Lie on your back with your legs up so your shins are parallel to the ground. Try to engage your core to get the curve of your back to become flush with the ground. Then slowly bring your feet down (either both or one at a time alternating) and tap your toes to the ground while trying not to let your back curve at all. Bring leg back up and repeat. Surprisingly hard and great to take pressure out of your low back!

Yoga & stretching, swimming & pilates are some to name a few. No matter what you do just make certain that your body is up to the task and don't ignore any signs it may give to you that you may need a rest or need to try a less intense exercise. When it comes to pain your body knows best!

For me it’s yoga. Make sure you listen to what your body is telling you, don’t push the forward bends and build your core slowly.

I do yoga, along with exercises from my chiropractor and physical therapist. For long term relief, you NEED ones that will strengthen your core muscles and ones that keep your spine flexible. So any exercise that requires using your abs is good- my thera pist said to even just tighten my abs whenever I'm using them, like lifting a milk jug. My chiropractor has me doing the "star" exercise program (you can google it) for flexibility, along with a roller to keep the muscles loose (Google yoga roller. You can find them at scheels)