Obtain a master's degree in criminology or criminal justice. Work as an employee or an intern at a courthouse, attorney's office or law enforcement department. This experience will give you an edge over other applicants when you apply to a doctoral program.
Investigate the doctoral programs in Criminal Justice offered by various universities by browsing the website of GradSchools and US News Education. Follow the links on these sites to get the contact details of universities.
Find out admission requirements at the universities where you wish to pursue your Ph.D. Pay attention to the Graduate Record Examination (GRE) scores that they specify. If you are a non-native speaker of English, you will also need to meet the required Test of English as Foreign Language (TOEFL) score.
Take the GRE test and TOEFL, if applicable. Check the universities to which you can apply with these scores. Apply to many programs, since admissions are highly competitive. Follow instructions and submit all transcripts, GRE scores, reference letters and the statement of intent. Include a curriculum vitae detailing your qualifications and previous work experience in teaching and internships.
Complete admission formalities at the university that accepts you and begin taking the prescribed courses. This will typically include mandatory courses in theories of crime, research methodology, policy analysis and statistical analysis and elective courses in criminal justice, criminology and other allied fields.
Take teaching assignments as specified by your university. Form your doctoral committee in consultation with your adviser.
Take the comprehensive exams at the earliest possible opportunity. These exams are designed to test your knowledge of the criminal justice system and your ability to interpret concepts. Clear these exams to move on to working on your dissertation.
Select the topic of your dissertation in consultation with your adviser. Choose a topic that will make a meaningful contribution to the existing knowledge base of criminal justice systems. Make sure this topic is approved by your doctoral committee before you begin your research. Work on your topic and document your findings. Write your dissertation in keeping with prescribed guidelines.
Submit your dissertation to the doctoral committee and make the changes they suggest. Perform well in your thesis defense interview to complete your Ph.D.