I've done precisely that in an Excel app before, which had a WPF front-end for large screen presentations. The thing you need to be googling is XamlReader. There are a few limitations with what you can do with that, but it's the easiest way. Of course you can also always create controls at runtime and use them to populate a form as required if you need something more complex.

As mentioned above, the Petzold book Code+Markup is definitely worth checking out if you want to get a feel for how to do this manually.