The academic job market is highly competitive, with an estimated two applicants for every faculty position available in philosophy departments, according to the Philosophy Department at Howard University. At a minimum you will need a PhD in Philosophy to be eligible for a position as a philosophy professor, but this alone will not make you a strong job candidate. Through planning and targeted additional work you can maximize your chances to secure a coveted tenure track position.
Obtain a bachelor's degree in the liberal arts. It is not necessary to major in philosophy, but you should take at least some philosophy courses as an undergraduate. Such courses will give you helpful substantive grounding in the field and knowledge of the areas of philosophy that will help you choose a graduate program that fits your interests.
Enter a PhD of Philosophy program. Most programs in the United States do not require a Master's degree, allowing you to skip the time and expense of obtaining one if you are certain you want to be a Professor of Philosophy. Choose a department with professors who share your areas of interest. Remember that you will need to form a dissertation committee and your dissertation process will be most successful if both you and your advisers are enthusiastic about the project.
Attend professional conferences early and often. Participate as a discussant or otherwise volunteer. This can get you into the conference at reduced cost and bring you to the attention of people who may one day be on the hiring committee looking at your CV. Start presenting as early as possible, even if you only have a poster or attend PhD colloquiums to network with your peers. Networking will bring you together with people you can collaborate with later and, again, get you known in your field.
Publish as often as possible during your graduate career and remember that articles in peer reviewed journals count for more than non-peer reviewed articles. Publishing with your adviser is good but also try to publish at least one paper solo or with a fellow graduate student as your co-author. Publications will greatly improve the impact of your CV at job application time.
Apply for any grants you are eligible for. Even if you don't get the grant, having experience in applying is valuable for your CV. Showing that you are a type of applicant who is more likely to bring grant money into your department will increase your appeal as a job candidate.
Complete your PhD and enter the job market. Ask your adviser to keep a watch for jobs that you would be a good fit for; professors often hear about job openings before they are publicly advertised. Update your CV and prepare your job talk carefully. If you make it through the first round of a job application, you will travel to the college for a day of interviews and a job talk. Research the department you are applying at and practice your job talk before the visit.
If you don't get a position as a college professor your first year, apply for a postdoc position and keep trying. It is important to continue to publish as you attempt to break into the academic job market.