Guys and gals, go for it or work away? Let me be very frank. Much as one doesn't simply walk into Mordor, one does not simply "become a professional philosopher." First, you will need a BA in philosophy or a related discipline. To get that, first you will have to pay money to take the SAT or the ACT or both. Then, once accepted, you will have to take a slew of tedious general education courses that have nothing to do with your major. Some of them may be interesting, many of them will not be. You will also likely have to pick a foreign language and take classes in it for upwards of two years, depending. As for your philosophy major, the classes you'll take for it will depend on the faculty. For example, if there's no one who does Wittgenstein in your department, then you won't be taking any classes on him. Some of the philosophy classes may be interesting, some of them will not be. Most philosophy departments also require their majors to take an upper level symbolic logic course. If you're not good at advanced logic, or if the professor is terrible, then expect to find this class highly frustrating and nerve-wracking. In addition to this, some departments require their majors to write a senior thesis.
If you graduate and did not receive a full ride or had no savings or other means to pay for your degree, then you will have accumulated many thousands of dollars in student loan debt. If you're not burned out by the end of the four years, then during the winter of your senior year, while finding the time in between finishing papers, you can apply to MA programs. To do so, you will need to pay an obscene sum of money to take the GRE and make sure you have a good writing sample, a well written personal statement, and letters of recommendation from your professors. When researching MA programs, you will notice that there are fewer of them than philosophy BA programs. They come in two flavors: funded and unfunded. Sometimes the funding is good, sometimes bad. If you apply to funded programs, these can be somewhat difficult to get into, because everyone else wants to be funded to go to school. At the MA level, you need not worry too much about finding a department that exactly matches your own research interests, assuming you have any at this point. A general fit is sufficient. Next, you need to determine how many schools you should apply to. You increase your chances of getting accepted by applying to more and decrease them by applying to less. If you apply to, say, ten programs, this could cost you a figure close to a thousand dollars. You will have to pay to send your transcripts, GRE scores, and whatever else programs want from you.
Getting into an MA program is not impossible, however, so let's say you do get accepted somewhere. First, you'll have to move there. Then, for the first year or year and a half, you will being taking classes. Some of them may be interesting, others may not be. In addition to this, you will likely be a teaching or research assistant. In the former case, you will be a grading robot. In the latter case, you will be helping a professor find stuff for his own research. Some programs let their students teach their own classes. This is usually intro to logic or intro to philosophy. Teaching your own class requires a gargantuan amount of prep time, especially when it's your first time. You may not like or be suited to teaching or you may like teaching. Even if you like it, grading is time consuming and procrastination inducing, and you will begin to wonder how it is the students in your class were ever accepted into a university, and indeed, why they were ever brought into this world. In your final year or semester, you will either take comprehensive exams, write a thesis, or do both. Exams require you to skim read a mountain of books and then regurgitate the ideas in them to your professors in written and oral formats. Writing a thesis requires you to write some fifty odd pages, give or take, on some topic you're interested in and your advisers are interested in, so it's best you nail down this topic early on in the program.
Assuming you graduate, then you can consider PhD programs. When researching them, you will quickly notice that there are even fewer of them than there are MA programs. Some of them may even post ominous statistics about how they receive two hundred applications and only accept five incoming students, causing you to think to yourself, "surely, given these numbers, there are well qualified candidates who are being denied." And you would be right. This thought then drifts into another: "How do these programs determine who makes the cut? At some point, they must resort to completely arbitrary and unfair criteria for cutting down the massive applicant pool." And you would again be right. If you are white, male, Christian, or conservative, then you may also begin to worry that you will be rejected if the admissions committee caught wind of any of these facts. Further along in your research, you will find that departments like engaging in a dick measuring contest, primarily thanks to a ranking system called the Philosophical Gourmet Report, whose man behind the curtain is a certain fat-faced, politically correct little gossip-monger named Brian Leiter.
You then notice that the programs on his list are those that have funding and can guarantee something approaching decent employment upon graduation. It's a riskier bet to apply to those not on it. So you apply to a set of PhD programs, with at least half on that list, though not to as many as you did MA programs, since you now want to be picky about which professors you want to work with on your dissertation, assuming you know what you want to write it on. If you don't know what to write on, never fear, just pretend to be original and creative. Let's say you happen to hit the jackpot and are accepted to a program somewhere. For the first two or three years, you will be taking classes. Some you may find interesting, others you may not. At the end of your third year, you will take yet more comprehensive examinations. Upon completion of them, you are usually awarded a superfluous second MA degree. In the final year or two, you are researching for and writing your dissertation, which is basically a book that no one will read. All the while, you will be a teaching/research assistant or teaching your own class (or classes!) and likely still have language requirements to fulfill. Furthermore, you will be expected to have at least one article, though preferably more, submitted for publication in an academic journal somewhere that, again, no one will read. This is merely to pad your resume and make you look good when applying for tenure track jobs.
Let's say you make it through five years of this. For the past eleven years, your undergraduate debt has been slowly but surely accumulating interest and may even have doubled. You now need a job to begin to pay it off and so start looking. You will find that the well of tenure track jobs is virtually dry and that you are competing with hundreds of other people just like you for the same tiny number of positions. Your suspicions of nepotism will also be raised when hearing of how other people landed such positions. Let's say lightning strikes twice in your life and you get a tenure track job. Now you must write yet more articles, publish a book, preferably more, and deal with the colossal bureaucracy of the modern university that will attempt to defund your department at every available opportunity, all while teaching upwards of hundreds of brainless vegetables the basics of philosophy. And voila, becoming a "professional philosopher" has been achieved.
My advice (as someone in an MA program in a related field in the humanities who has applied to PhD programs but is seriously thinking about dropping out of academia completely, even if he is accepted somewhere): you don't need a degree to be a philosopher. Find something tolerable to pay the bills, if possible, and pursue philosophy on your own time.
Relevant (and funny and true, although I do think Marxists have, in part, contributed to ruining higher ed):