What relevance do law school grades have on admission to a Master's degree in economics? I am currently a rising 2L law student who passed up an opportunity to do a joint JD/MS in Economics. I didn't think I was adequately prepared to take on the Economics degree, though. (Not enough math background.) I am considering pursuing a master's degree part time after finishing law school, though, because it seems to be more interesting and more valuable in the job market than law.

What bearing will my law school grades have on admission to a master's program, and would that calculus change if I took the requisite math courses (Calculus I, II, and potentially III,), as well as a remedial stats course?
The effect of your law grades probably depends a lot on the program you are applying to. I guess (really just a guess here) the overall GPA might in most cases serve as a signal for being a good/bad student, so they probably matter.

I think it doesn't really matter what the courses are. Most law courses have nothing in common with economics courses even if they cover the same topics. And to be honest, people are lazy and probably are not try to figure out which of your courses are useful for an econ degree. That is of course different for a law/econ master or a specialized econ master.

However, most master programs require you to have a sufficient knowledge in math.

But, as I already said that depends on the university/department/program.
So, my advice would be: ask the top 1-3 universities on your list what the necessary conditions are.

A minor remark: I can't think of my econ MS being useful in a real job (i.e. not governmental or in academia) but maybe that is just me. Maybe don't pick a research master's degree.