This is one of the profiles in the Administrator (AD) open competitions, though in some cases Assistant (AST) exams may have an AST3 legal policy officer or law-related profile announced for more technical positions. Legal affairs officers are required to have a relevant diploma in law. Decision is always made by the Selection board on the admissibility of the diploma. Lawyers are mainly employed by the European Commission, the European Court of Justice or the European Data Protection Supervisor, but any other EU institutions may offer positions for those who passed a recruitment exam in law.
See also:
Auditor, Economist, Statistician, European Public Administration, Linguist, Translator, Interpreter
Related link:
Tips and Tricks, EU Agency Selection and Recruitment Database