I'm on the job market now. I will recommend a book that will answer your question. This book will give you an accurate state of the academic job market as it exists today. This book is dead on accurate.

https://www.amazon.com/Professor-Essential-Guide-Turning-Ph-D/dp/0553419420

(I have no affiliation with the author)

/r/askacademia is also a good sub to ask this question, as it gets asked quite frequently and they'll probably have equal archived posts from which you can peruse.

I always like to quote Obama's message to his interns:

"Worry less about what you want to be and more about what you want to do."

If you're focus on the being (i.e. being a professor), you end up making sacrifices along the way of what you want to do (i.e. history) because being and doing are not the same thing. The being is the title, the doing is the action.

I can tell you now as an MA student that being a professor does not guarantee you'll be doing any more history than someone who just loves history. Administrative tasks, teaching, networking, take so much time out of your day that its rare you have the time for research.

This is not mentioning the essential problems of the difficulty of getting a job as a tenure track professor. If your goal in life is tied to being, then not BEING a professor sets you up for an identity crisis. If you're focused on the doing, you can do regardless of what job you have to perform to make your rent.

In my field, Late Antiquity, some of the best scholars are independent scholars. I just found out from my advisor that one of them, who's very well known considered The Expert on an ancient source, who publishes extensively, works as a secretary full time. I also heard that a major contributor to early christian studies is someone without a PhD who is an engineer in his day job. He just happens to have the funds to pay for access to all the essential libraries and journals he needs to research. I promise you their lives are not any less satisfying.

Since you're entering college, this is a good time to think about these questions. College opens you up (or it should, ideally) into a variety of opportunities for intellectual exploration and careers. Learn from the beginning that in this modern world, the two are separate more often than not (it didn't used to be this way, but it was a different economy in our parents' day).

Think about your doing vs. being question, and find a way to thread both.

Btw, I'm about to enter into a Ph.D. in the study of Late Antiquity. I have no illusions about my ability to get a job at the end of this Ph.D. and kind of view it a bit like a suicide mission, i.e. there will be no job at the end of this.

But I love this field. Love it love it love it. I love the research, love my professors, love my colleagues. Even as i do this Ph.D., I'm keeping my eye out for alternate career skills, and alternate ways to stay in touch with everyone, research, publish, and present.

This is the new world we live in. You can no longer make your life being and doing in one package. But it doesn't mean you have to stop doing.

EDIT: BTW, if you want to know what actually doing academic history, I can sum it in a nutshell as: "reading and then arguing (with your peers)." The professional field is built on arguing rather than knowing, or rather, knowing as an extension to arguing. It's not a coincidence that the fields of history and lawyering were tied very closely in the past.

Teaching is considered a separate discipline. That's "knowing and adapting (for those with less knowledge than you)." Obviously the two help each other and are related, but I find that they use different parts of your skillset.

So with that in mind, consider which aspect you like more.

In addition to what everyone has already said and linked to about the state of the academic job market and the odds of becoming a professor (tl;dr: it's terrible and your odds are single figures, at best), I don't think you should invest too much, either in terms of time or emotionally, into this career path. If you're just finishing secondary school, then you'll need to remember that you've never experienced university life or academic history before, let alone historical research (which is the most important part of your career). Academic and university-level history are very far removed from secondary-level history and you may find that it's not what you wanted to do with your life. At the moment, you're like someone who dreams about being a concert pianist, but not only have you never touched a keyboard (you've never done academic research), you've also never even been to a concert (spent significant time in a university); your entire dream is based on a love of listening to music and watching musicians in movies.

I hope I don't sound discouraging, because that's not my intention. There's nothing stopping you from becoming a professor. But make sure to keep things in perspective. You're going to grow and develop and change a lot, both intellectually and personally, over the next four years. If you still want to be a prof at that point, then the advice in this thread will be a lot more useful.

This question comes up occasionally here. There was a recent Monday Methods on deciding whether to go to grad school with a lot of great input from u/restricteddata and u/khosikulu. You should also check out Will I be able to find a job as a historian? and Those who have a degree in history, what is your occupation now?.

(Note: I'm writing this from the USA; I'm not sure where you live. If it's the UK, the specifics of this advice might look a little different, but the general outline of what I'm writing will still apply as the US and UK job markets are pretty similar.)

A PhD in history will open a lot of doors to you. Currently, fewer than half of history PhDs in the US will secure a job as a professor. The rest of those PhDs go on to have rewarding careers, however, in non-profits, government agencies, and other careers in which research, writing, and speaking skills are prized. You will not become wealthy with a history PhD, but you'll have many options for a rewarding career, and these will put food on your table.

That said, the path to becoming a professor is...harrowing. Depending on your specialization, the job market is currently absolutely brutal, and this is unlikely to change in the near future. One ancient history job this year had 200+ applicants for a single position, and most were extremely well qualified. It's not uncommon for jobs in my field (ancient / medieval) to have over 100 applicants. Are you capable of being in the top <1% of all history PhD graduates? Are you willing to invest 10 years of your life trying to get to that point?

If you want to be a professor, consider specializing in Asia or Africa. The job market isn't equally bad across all fields. Currently, there are far fewer PhDs who specialize in Asia and Africa, and I think this will probably still be true in 10-15 years (Asia isn't a fad; as China takes over the global economy, we're going to need more people who can teach Western students about its history). The same school that had 200+ applicants for a job in ancient history had about 40 for a professor who could teach about the Pacific. US history is glutted and always will be. European history is not much better. Latin American was a growing market, but we might have hit the saturation point, and I can't predict how Middle East historians will fair by the time you'd have your PhD. World History is trendy right now, but will it still be in 15 years? Who can say. But if you study Asia, you'll be much more likely to land a professorship -- and you'll have some awesome alternative career options with that degree.

However, this is all a bit far in the future for you right now. You can do a lot of things with a history + English degree, grad school being just one of them. My advice would be to spend your years as an undergraduate learning languages in addition to taking your history courses. Pick up Chinese, Japanese, or something else that could set you up to study Asian or African history. If you're dead set on studying US or European history, learn French, Spanish, or German (if you want to be a medievalist, learn Latin!). If you continue on to get a PhD, these languages will be very helpful (historians read lots of things that aren't written in English, so you'll need to be good at languages to finish your PhD). If you choose to go a different direction after graduation, you'll have language skills in addition to research and writing skills, and that will give you more options.