I can speak from experience that it definitely will. Last month, I updated my MBP that was still running Snow Leopard (and on which I type this as we speak) to El Capitan via a bootable drive. I backed everything up via an external hard drive and restored everything once I updated to El Capitan. After that, I was able to update my computer to Sierra without issue. It's been smooth sailing ever since, except for a few minor hiccups with my music on iTunes (which I've since sorted out).