Note: I have tried to use People control under General and rules are working perfectly for that control but the issue is it is taking too long to resolve the username which makes me to go for Legacy people picker control.
Solved! Go to Solution.
I was in the same situation a while ago. I had to find a solution quickly, so here is what I did :
Hopefully this will help.
I have found an another solution, created that list column as mandatory so by default the legacy control had that validation applied.