If you're looking to rule over the judicial system with an iron fist in BitLife then you're going to need to do a whole lot of schooling and lawyering to achieve such a thing. This career path is a requirement if you are looking to complete all of the achievements in the game, so you will want to try this at least once if you are trying to get another check-mark for your list.
How to be a Judge
To become a judge in BitLife, you will need to be a high smarts character, complete college, and then go to law school to become a lawyer. You will then need to maintain a job as a lawyer for a total of 30 years to get access to the judge career. Once you see the option for Magistrate, apply for that and you will become a judge!
Tips & Tricks
When you create your character you only really care that they are smart. Try to start off at 80%+ smarts, and you can work at increasing it as you age. Go ahead and go to the library, read books, study harder in school, and meditate to attempt to increase your intelligence. Keep doing these each year as much as you can stomach.
In school, make sure to study harder each year, and once activities are available, make sure to join at least 2 or 3 per school type. You will get a chance to join these in Middle School and High School. Doing these extracurricular activities will give you a better chance at getting a scholarship.
Once you graduate from High School, look for the Political Science major as an option. This guarantees you can get into Law School, so if you don't see it you can close out of your application or age up a year to see if it is offered. Once you find it, do the same thing with activities and studying in college.
Now that you've graduated from the University, you can now go to Law School. You should be able to get a scholarship, but if not just take out a loan. You shouldn't really need to do much studying, but you can just to be safe.
When you finish with Law School, it's time to look for a job. Go to the job menu and find the Junior Associate option. When you've gotten the job, make sure to work harder each year to get promoted a lot quicker than you normally would.
You just need to age up now and continue getting promoted at your job. You now need to complete 30 years as a Lawyer to become a Judge. If you've stayed at the same place, you can check how long you've been there by clicking on the Job menu and then tapping on the performance tab.
Once you reach the 30 year mark, just look for the Magistrate job option and apply for the position. If you've maintained your smarts and gotten this far you should be able to finally become a judge! Work hard at dulling out sentences for a few years and you should get credit for the achievement.