The key thing, which @daniel alluded to, is that whatever html gets generated, whether JS is enabled or not, must be semantically correct so that assistive technology (such as a screen reader or braille device or screen magnifier) can understand it.
If you have important elements of your UI that are created on the fly in JS, and JS is turned off, then your page might not be accessible to some users, so in that respect, you would have to support a non-JS browser, but only because of the way you coded your page. If all the important elements are there without using JS, then you'd be ok. So it's not really a statement of whether non-JS browsers need to be supported, it's whether your html will be complete and usable without JS.
Update: November 14, 2018
Great discussion in the comments. It's a simple question but a complicated answer. I've read the conformance guidelines at least a dozen or more times thinking about this post (and thus delaying my reply).
@TripeHound touched on a key point,
If insisting on JS for the site to work is acceptable, and you pass WCAG with JS enabled, then everything is OK.
as did @Daniel,
if JS is disabled but it passes all criteria when JS is enabled (ha! Never happens)
that if the JS-supported page conforms to WCAG, then you can state that you rely on JS and you would not have to support a non-JS page. But again, that's only if your resulting JS page was conformant. If it was not conformant, then you would have to support a non-JS version.
So the short answer is the dreaded "it depends".
It's also worth reading WebAIM's take on this subject.
WebAIM's statement helps, but it's not authoritative. Certainly their opinion is based upon the guidelines, but just because someone states something, it doesn't make it true. Fortunately, if you read (and re-read) the conformance guidelines, in particular requirement #5, I think WebAIM's statement says the same thing but in plainer English.
And they have a somewhat expected qualifier:
This qualifier is somewhat alluded to in my original answer.
Given that the OP is 3 years old, I'm not sure anyone (other than us 3 :-)) will see this discussion. But I learned something.