Some celebrities will hire a specific makeup artists for all of their shoots. I'm talking about huge stars like Tom Cruise or Kurt Russell. In fact, Kurt Russell has been with the same makeup artist for decades. In Guardians of the Galaxy 2 there are de-aging effects on him, most of which were accomplished with the help of practical makeup from his personal makeup artist. Let's not pretend like that makeup artist isn't make big bucks.
One unfortunate aspect of this job is how you break in. You can either take classes to get a certification, which you may have to do if you're working with effects opposed to just simple makeup, but that certification may not guarantee jobs. Most people have to work for free to start their career and get credits. That also means using your own makeup for free.