Perhaps you mean that by civil law he is married. By Church law, he would not be legally or validly married.
Also, it appears that this priest is a secular priest (he works at a parish, and does not appear to have initials after his name.) Secular priests make promises, not vows.
But yes, he would need to be laicized first, and on top of that, would need a dispensation from his promise of celibacy to be legally married in the Church.
As for excommunication: I don’t think we can say “it doesn’t matter” if one commits a sin while excommunicated. Sin is still something to be avoided, whatever one’s canonical status, and one should be particularly vigilant against committing sins if one has no access to the sacraments.