Greetings, aspirant!

In order to join the CBI, one must appear for the UPSC civil services examination and be selected in the IPS department. Then you can serve in your cadre for a certain amount of time and join the CBI based on recommendations. This route requires hardwork and dedication and even then, is not a guaranteed success. But that's not to say that you won't have a really prestigious job anyway, as you're a part of the IPS department of the country

Apart from UPSC-CSE, you can appear for SSC-CGL and apply to become a sub inspector in CBI. From here onwards, you can work hard to get promotions and eventually become an officer.

You should know that this is by no means an easy career path, however, it's not impossible either. You will have to work very hard and stay focused if you wish to become a senior ranking officer in the CBI

Hope this information helps

Best of luck!!