It is a criminal offence in Malta for a person to marry more than one person at the same time and it is irrelevant whether such marriage was contracted abroad. Bigamy is prohibited by Article 196 of the Maltese Criminal Code. Separation does not entitle a person to remarry, hence contacting marriage whilst separated also amounts to Bigamy. A person who is married can only remarry after obtaining a divorce or an annulment.
It is a defence for a person accused of bigamy to argue that the first marriage was null. Hence pending criminal proceedings for bigamy one could institute legal proceedings to annul that marriage in order to have that marriage declared void.