This question came up after one of my professors mentioned last semester that most PhD (or even master level) trained historians would reject a consulting offer from the History Channel (or any of the Discovery Channels etc.) as it would be career suicide. (I know that this is probably a contentious statement, but beyond the scope of this post)
I began googling some of the "historians" that are interviewed on some of the History Channel programs and found that most of them are not PhD trained, and many don't have any grad school experience. One of the sources which they cited as a "medieval weaponry historian" (or something along those lines) was very involved in renaissance fairs, a competitive archer, and a IRS manager. Is he an historian?
What level of training/practice do you think is necessary to call yourself a "historian"? In my mind I've always thought of historians as graduate level trained and currently researching/contributing to the field. Is this unrealistic?
It depends on the beholder. Am I a historian? I'm a Mathematician/Statistician Undergraduate but I have 36 total books which I have read at least 3/4th read of and most of them are complete; I have another 5 or 6 which are incomplete. Many of them are legitimate college textbooks on these subjects and have costed hundreds of dollars, and some such as David Chandler's or John Elting's works on the Napoleonic Wars are basically the most advanced, comprehensive works on those subjects in existence outside of PhD papers on the topic (and arguably even then).
Does reading all of these make me a historian? It depends, again, on how you think or define what a historian is. Is a historian someone who progresses the field of research and comes up with new research or modifies/improves old research? Then by definition only graduate students and PhD graduates can be classified as 'historians'. Do you classify anyone with a high academic knowledge of the topic a historian? Is a 'popularizer of history' a historian even if they aren't trained or educated in any specific thing? (ie: John Green, Dan Carlin).
I've seen results from both sides of the fence from both PhD/Masters holders and not. I personally take hold that if you don't produce actual new academic work on the subject you can't call yourself a historian -- I believe contribution is necessary so by that respect I don't believe I'm a historian. It's just a varying plane of opinions though. Someone may consider someone who makes authentic medieval weapons and uses them along with period correct clothing/armor regularly and indulges themselves in that period of time as a historian of that time, some won't, clearly History Channel doesn't care though.
TL;DR:
It depends who you ask. All that matters though is that you don't need a PhD to be a student of history or to help others come to a fuller understanding of it. You don't need to dedicate your entire financial and adult life to it to be a student and lover and even teacher of it; you just need one to push new bounds and discover 'new' history. It's why non-degree holders can post here: You don't need a degree to read a shit ton of academic works and get an intermediate knowledge of the topic you just need one (or be in the process of getting one) to get the funding to do new shit and to really dedicate your life to really specific, nuanced, new topics.
You can be a historian without a Ph.D. That said, you probably would have trouble working as a historian at a University without one. A Ph.D. is a lot of work, and people who have them are prone to look down on people who don't have them, to question their seriousness and credentials, etc.
The proof of doing good history, however, is in winning the attention and/or respect of the field of history as a whole. Pharmacist Jean-Claude Pressac made a big stir in holocaust studies, and microbiologist Brent Mueggenberg has just written a good book on the Czechoslovak Legion. I'm sure there are other examples.
The History Channel, meanwhile, is not a good place to look for historians, because it's not a place to find good history. Let me also take this chance to say this: if you watch a Hollywood movie that claims to be "based on a true story," then you should interpret that as "fiction."