Equity strategy career path - good to join as junior?

I did equity research and M&A before. Also wrote two theses, one on a stock market strategy. Overall, I don't think M&A really was that much of a prerequisite though. In the team I worked in, people who had previously joined were mostly from equity research or actually macro research (ie working as an Economist).

Short,

Everyone I know that works for our division's CIO either has done portfolio management, or has either a trading or research background giving them some insight to the markets.

I also know a guy that went from product management to trading to equity strat. I think if you can check the successful trader box, you should be good in a lot of cases.

Does anyone get into equity strategy straight out of undergrad as their first job? Not to give too much away, but I have the unique opportunity to start on that path this summer and thinking about career as strategist. Is ER or trading beforehand necessary? Should I opt for trading next summer instead?

Yes, that can happen. ER is helpful, but I really don't see why you would need trading. Trading doesn't have that much in common with investing, which is pretty much what equity strategy does. It makes a lot more sense the other way around, as you then understand how something might affect the markets and when to maybe take a proprietary position. If you have the option to go into it and want to do it, then go ahead. Nothing's stopping you. You can always try trading later on, although I wouldn't wait too long. Most people who go into trading join at a young(er) age.