To some extent, “exciting” criminal justice jobs are indeed a fantasy crafted by television shows and films. There are likely going to be moments of excitement on the job, but it’s not likely to be your day to day experience. There aren’t many jobs where you’re going to spend day after day investigating murders and other high-profile crimes. And in reality, if you actually did, you probably wouldn’t handle it well psychologically. That’s another thing that’s unrealistic about these shows. Most of these characters should be dealing with all kinds of PTSD, and aren’t. Real life isn’t like that. In real life, being put in traumatic situations does take a toll on your mental well being. Some dull office work between “exciting” investigations is actually a good thing.
If you go into criminal justice, you can expect to start with rather tedious tasks. You’ll probably begin work as a patrol or probation officer or another correctional officer. This is a stepping stone on the way to becoming a detective or undercover agent. Even officers who work directly for the government (like in the FBI) usually have previous experience working in a state police outfit doing mundane work. Military experience may also help out as a prerequisite (not to the point you should pursue it if you don’t already have it, but if you do it could help you move forward).
Those government jobs which are most difficult to get are the ones in the federal government. This is largely because of the nature of crime. The majority of crimes can be resolved on a state or local level, which means that the majority of officers find jobs with state and local agencies. You don’t necessarily need a higher education degree to get a job with a state or local agency, but you do need a bachelor’s degree or higher to get a federal position, along with previous experience in a state or local position (or military experience).
So to increase the odds of getting an “exciting” job, you should probably pursue a degree course in criminal justice or a related field. Specializing in something may help improve your chances as well. For example, a degree in chemistry might help you to get a job in forensic investigations or in arson-related work. A degree in psychology can help you to get jobs pursuing or rehabilitating criminals with psychiatric issues. You might even try a dual major in criminal justice and chemistry or psychology.