Article from https://www.angloinfo.com/how-to/greece/family/marriage-partnerships/marriage-requirements
The process for getting married can vary slightly between regions and islands so it is suggested to verify requirements with the local City Hall, and/or with the presiding religious leader in the case of a religious ceremony. The application process may take a few weeks so it is important to start as early as possible.
A wedding notice must be published in one local newspaper or (in small towns) posted at the town hall in the Greek language eight days before the application for the marriage licence can be submitted. One notice must be published or posted for the bride, and one notice must be published or posted for the groom. The names on the notice should be phonetically written in Greek and not in Latin characters.
The following are required of foreigners applying for a marriage licence in Greece (the bride and groom must each submit these documents):
Two sets of the above documents are required if both civil and religious ceremonies are to be performed. One set is for the town hall and the other for the priest. Note: Americans marrying in Greece may be able to use a valid marriage licence issued in the United States if the licence does not contain any wording that indicates it is exclusively valid in the issuing jurisdiction.
For foreign nationals already in Greece, it may be possible to obtain a Certificate of No Impediment from their consular authority in Greece. This will usually require the applicant to attest to the fact that they are legally able to marry. A minimum residence period in Greece may apply, and the waiting period for the Certificate can be several weeks. In some cases, consular authorities may require proof of civil status from the person's home country, which can be obtained from the registry office or town hall of the person's previous place of residence. This must be officially legalised with an Apostille stamp. Note: If a Certificate of No Impediment cannot be obtained from a consular authority in Greece, then it must be obtained from the local registry office or town hall where the foreign national resides, therefore it is strongly suggested to contact the consulate in Greece well in advance.
Any foreign legal documents which are to be used in Greece must be officially legalised with the Hague Convention Apostille. The Apostille is a stamp or seal that signifies the document is legal and authentic; it is meant to simplify the process of document legalisation across international borders. If submitting more than one document requiring a Hague Convention Apostille, each document must have an Apostille. A Hague Convention Apostille for a legal document, such as a birth certificate or divorce decree, can be obtained by an approved government office in the country, state or county where the document originates (this could be a State Secretary's office or Foreign and Commonwealth Office). If the country is not a member of this Hague Convention, then a certified letter from the town hall where the document originates, stating that the document is valid and true, may be sufficient. Otherwise, the Greek Embassy in the applicant's home country may validate the documents.
All legal documents submitted for the marriage which are not in Greek must be officially translated into Greek. The term official translation means a translation that has been made and certified by a lawyer, a certified translator or by the Greek Foreign Ministry’s Department of Translation (μεταφραστική υπηρεσία/ Metafrastiki Ipirresia). For those outside of Greece, the Greek Consulate in their home country can offer official translations. A fee is payable for translation services.
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All marriages in Greece, whether civil or religious, must be registered at the local Registrar's Office/Office of Vital Statistics (Lixiarhio) within 40 days following the ceremony. Registration can be done by the bride or groom, or by any individual who is in possession of a power of attorney signed before a Notary Public giving them the authority to register the marriage. Once registered, a Marriage Certificate (lixiarchiki praxi gamou) will be issued within three days and can be picked up or sent via the mail. Note: Marriages not registered have no legal validity. After 90 days, marriages can only be registered with the District Attorney's authorisation and the payment of fines.