Documents necessary to be married in Turkey:
1. Marriage petition (Evlenme Beyannamesi).
2. Certificate/Affidavit of Eligibility to Marry (Evlenme Ehliyet Belgesi): either a marriage license from your own country, or a statement from your country's consulate or embassy in Turkey that you meet your country's requirements to be married.
3. Personal identification (passport, identification card, birth certificate or health certificate, as required by the authorities).
4. Photographs of the bride and groom (five copies of each) for the official records.
You see that you probably already have one of the required document—your passport. Another, the photos of bride and groom, should be easy to obtain well before you leave home.
You'll also save money, time and trouble by obtaining a marriage license from the appropriate authorities in your own country before coming to Turkey. If this is difficult (because you are already in Turkey), you can obtain one from your country's embassy or consulate in Ankara, or perhaps in another Turkish city (depending on where your country's consulates are in Turkey).
Please note that if your own country won't allow you to be married, Turkey will not allow you to be married.
That leaves only the Marriage petition to be obtained in Turkey.
The US Consulate-General in Istanbul's website Getting Married page has lots of good information useful to anyone of any nationality wanting to be married in Turkey. Be sure to also check with your own country's consulate.
If you plan to use travel services for your wedding (hotels, flights, cars or vans, wedding facilities, catering, etc.), my friends at Travel Atelier, a TurkeyTravelPlanner.com partner, can make all those arrangements and may also be able to help with the legal paperwork.
—by Tom Brosnahan