Non-STEM Letter of Rec for STEM PhD Programs
It's important that you show potential for research in your application including letters of recommendation.
For me, I had three letters, two from people I did research with as an undergraduate, and one from a history of science professor I had taken a couple courses with (definitely a more &quot;history&quot; slant than &quot;science&quot;).
That worked for me. No idea whether it will work for you because ultimately it will depend on who reads your letters, what they say, and what the rest of your application says.
Remember rule #1, and then go from there:
It's important that you show potential for research in your application including letters of recommendation.