So I've been working at my current employer for almost 4½ years. A while ago I was approached by a manager from my previous employer asking me if I would be willing to assist them with some projects as an external consultant. It turns out they don't have the required knowledge in-house and since I had already worked on those projects when I was employed with them, they turned to me.
Since they would require me to do things I already do for my current employer, I agreed. We still have to agree on the details, like payment and exact expectations, but I've already made it clear I would only be able to help them outside my regular working hours and my main job would always get priority over them.
I'm now wondering if it would hurt or rather help me if I were to mention this to my employer. I don't think I have anything to lose by telling them as my contract doesn't mention disallowing anything like this (as long as I don't use their resources or things I developed for them of course).
I think that mentioning this might let them know other companies are looking for people with my profile, which might reinforce my position in the company (improving chances of raises or promotions). I am certainly not someone who couldn't easily be replaced, but still.
Finally I want to clarify that I am still very happy in my current job and am not looking at leaving them to become a full time consultant, nor do I have any intention of going back to my previous employer. I would only do it for the experience and to earn a little extra on the side (increased taxes and stuff taken into account). I would also make this very clear to my boss if I told him about it.
EDIT: ALready some great answers, but I feel like I need to clarify some things:
- My contract, company policy and the law all permit me to do something like this, I have checked this before I even talked with my previous employer.
- I am not, and certainly will not be planning to leave my current employer to go back to my previous employer or to become a full time freelancer. Working with them is still very fulfilling and I have zero complaints. I would also make this very clear when approaching my manager.
- If I were to tell my manager, I wouldn't do it with the intention to gain anything, it would mainly be because I don't want to do it behind their back.
- Even though I would be doing the same type of work, my previous and current employer are in completely different fields, so I wouldn't be working for a competitor. The work relates to a specific branch of IT which is used in a lot of big companies.