I've had migraines since I was 13 and there were times I had to leave early (if it was really bad, I'd go straight to the ER) or call in if one hit me hours before I was supposed to be at work and I couldn't get it under control. If you know your triggers, do your best to avoid them. Get frequent sips of water or fluid, keep snacks handy if you get 5 minutes of calmness to keep your blood sugar from crashing, etc. My rescue med is Relpax, so I would have a couple of tablets in my purse and I kept Excedrin Migraine as well as ibuprofen in my locker; if I felt like my headache was a migraine (mine are without auras), I'd take Excedrin Migraine or high dose ibuprofen (600-800 mg per my doc's advice) first and if that didn't help, I'd take my Relpax an hour after Excedrin or ibuprofen.
You do NOT have to disclose your migraines during interviews and I wouldn't do so.