I can only answer for my own country, and you did not specify where you are from?

Here in Scandinavia I am afraid the answer is undoubtedly that you need a PhD to be a professional historian working at a university. Even a PhD is is far from a guarantee of becoming a tenured professor of history.

That being said, a MSc may well qualify you to be somebody's research assistant, to be a history teacher, a writer of historical fiction, a popularizer of history, running a history website, or combine it with a degree in language, archeology or even biology where history is useful and is drawn upon for a lot of weird niche jobs and research projects you never even know exist until you are in an environment where you start hanging out with historians, linguists, archaeologists, sociologists, anthropologists, biologists and other researchers.

So it all depends on your aptitude, initiative, willingness to take risks and what you actually want and mean by being a "professional historian". No department of history I have ever seen would consider hiring an MSc as a historian, but there is life outside of University and a lot of research depends on weird crossdisciplinary skill sets.

u/crrpit recently answered a question about what defines a historian, and I personally did one about careers in history. In general, most people who make their livings as "historians" are university professors or researchers with PhDs. Their employment at universities typically entails some responsibility or expectation to publish new papers, books, or other research in addition to teaching responsibilities. That's going to cover the vast majority of people who describe themselves as historians, and those positions typically are not available without a PhD. In my opinion, the single most important qualifier that u/crrpit described was " creating historical knowledge." There's nothing that prevents someone without a PhD from formulating new theories, interpretations, or concepts in a historical field. There are plenty of people who produce valuable research with only their MA, or less. I have certainly found MA theses that turned out to be useful or interesting sources. That said, it is much, much harder to do that as a profession because universiteis are the primary organizations willing to pay you to do it, and they mostly hire PhDs.

That said, most of the jobs I described in my answer about careers and (as well as the careers in museums or high school teaching that the questioner wasn't interested in) are available with only a Master's degree. Like I explained there, some of those jobs entail very different sorts of work or even different specialized Master's degrees rather than "history." That said, they all provide the opportunity to work with history or apply your knowledge of historic research.