In order to become a constitutional attorney within the United States, you must first graduate from law school and become a licensed attorney. You then must be sworn in to practice law at the federal level. Finally, you must begin representing clients in constitutional law cases, or cases in which a question of constitutional rights is being disputed.
First, to become a constitutional attorney, you will need to go to law school. Admission to law school is based on your undergraduate GPA — a four-year bachelor's degree is required — and on your performance on a law school aptitude test called the LSAT. Getting into a top law school can be competitive, and you will usually want to get a degree from a school with a good reputation in order to get a job in a law firm that handles constitutional law questions.
During law school, you will want to take classes that help you become a constitutional attorney. Some schools offer specializations in constitutional law, while others offer only general law degrees. Regardless of which school you choose, make sure you take classes in constitutional law, as well as in federal civil procedure, since constitutional law cases most often take place in federal courts. Constitutional lawyers are also litigators — which means they must go to courts and speak in front of the court to represent clients in cases — so taking moot court classes can be useful to help you develop the skills necessary to become a constitutional attorney.
Upon graduating from law school, you need to be sworn in. First, you will have to take the bar exam in your respective state, in which you demonstrate your knowledge of constitutional law and other areas of the law. Then, if you want to work on the federal Constitution — which is what most constitutional lawyers do — you will need to be recommended by an attorney and sworn in to practice law in front of the federal courts of the United States.
After being sworn in to federal court, you will need to start working on constitutional law cases if you want to become a constitutional attorney. You may wish to got to work for a large law firm that handles constitutional issues and disputes. You generally will need to work your way up to become a constitutional attorney, starting by doing research to assist other constitutional attorneys and eventually gaining more knowledge, skills and experience so you can get your own clients and actually get to make arguments based on the Constitution before the federal court.