PhD in mathematics, science communication jobs I'm doing a PhD in mathematics at one of the world-leading universities. I spend a lot of time engaging in science communication: both speaking (talks for general audience, some of them quite successful) and writing (popular science blog, I started to publish also in some magazines). Even though I enjoy maths a lot, I prefer communicating it to non-mathematicians much more.   

Would getting a job in science communication as opposed to continuing research or working in industry be a "waste" of PhD? 

Also, would I need a degree in journalism or science communication to be considered a serious candidate for jobs in popular science or media? I've done some research online but it seems that there aren't many scientists (not to mention mathematicians) with a PhD who would focus their career on communicating science.
A PhD is only "wasted" if you believe it is wasted. If you enjoyed your research, and it's helping you to engage in a long-term career you enjoy, why would it be wasted? 

However, there is a very clear need for people with solid scientific backgrounds who can clearly communicate complex mathematical and scientific ideas to the general public. People who can bridge the gap—for example, explaining concepts like "herd immunity" or "cryptocurrency"—in ways that the public can understand, are valuable in the scientific community, and we should be encouraging people to make that kind of outreach. It's not as popular as it should be in academia, but I believe that as more people engage in such careers, we will see room for growth. 

So if it's something you really want to do, go for it!