An undergraduate degree usually isn't enough for a job in much unless there's kind of an explicit promise you'll be qualified at the end (law, medicine, dentistry, nursing, engineering, etc).
To be a professional philosopher you would almost certainly need a PhD. This would allow you to teach inside universities and do research. Of course, there is no promise of a job at the end of it. Alternatively, you could be an author but its quite the struggle to initially get published and even more-so to be successful. The only other career that is directly related which i can think of is teaching it in a highschool setting (there is VCE philosophy).
If you look at a lot of the top professors, they were either rather talented/lucky here or went abroad to the most respected institutions to get their PhD (Cambridge, oxford, etc). I assume there are more philosophy PhD's in training by professors than there are spots for professors. A professor may train 10 students who want to take his one job eventually. Of course, you can see this is rather unsustainable.
The vast majority of people with a major in philosophy end up in other fields but it still is possible (albeit not likely) to end up in a field that is directly related to it.
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