A visionary is a person with a clear, distinctive and specific (in some details) vision of the future, usually connected with advances in technology or political arrangements. Examples would be Buckminster Fuller in architecture, and some of the pioneers of personal computing. A visionary may function as a secular prophet, emphasising communication and a figurehead role, rather than implementation.
Visionary art is defined as a category of primitive art (i.e. art of those not formally trained). Artists may produce art categorised as 'visionary' for its luminous content, without being primitives in any sense (e.g. Samuel Palmer). An artist celebrated for his visionary, religious take on ordinary life is Stanley Spencer.