A writ of habeas corpus is a judicial mandate to a prison official, usually the warden, ordering that an inmate be brought to the court. Habeas Corpus, in the Federal Court, is a petition that claims that you are being detained against your US constitutional rights.Habeas corpus protects United States citizens from unlawful or indefinite imprisonment. To get a writ of habeas corpus, you must file a petition for a civil (not criminal) proceeding in either state or federal court. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment. A Writ of Habeas Corpus is a civil proceeding that is available in both State and Federal Court to challenge the legality of imprisonment. Because the purpose of the petition is to gain the release of an unlawfully detained person, the reasons that justify the writ are narrowly defined. A Writ of Habeas Corpus. The basis for such an application is DRL §70. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment.