Jewish law does not require that marriages be performed by a rabbi – only a person sufficiently knowledgeable to perform the ceremony is necessary. That said, state law is stricter and varies considerably from state to state. Most states require that a licensed member of the clergy perform the wedding. Some municipalities, like New York City, insist that clergy performing weddings be registered with the city. Sometimes, if a couple wants a particular friend or relative to perform the wedding who does not meet the requirements of the state, they can use that person’s services and also engage a rabbi or other licensed individual to sign the appropriate documents.
Many rabbis will only perform weddings for members of their synagogue and their families. You may have to join a synagogue if you want a particular rabbi to perform your wedding. However, there are many other rabbis who do not serve as congregational rabbis, who often perform weddings. In addition, there are independent individuals in many areas who perform lifecycle ceremonies like weddings. To find an officiant, ask around and seek the advice of friends. You can also contact the local board of rabbis which will have a listing of all rabbis in the area.
You should meet with whomever you plan to engage as an officiant before you do so. It is important to discuss his or her religious requirements for a wedding and his or her philosophy. You will want to find out if you are simpatico before you move forward. Questions to ask include: basic religious requirements, areas of flexibility, how many pre-nuptial sessions will be required, and general philosophy about weddings -- can the couple design their own ceremony or will the rabbi arrive with a pre-packaged ceremony? If he does, is there room for flexibility? Most rabbis or other clergy will charge a fee to anyone who is not a member of their synagogue. This is also something you should ask about upfront – most locales have a going rate.
Finally, a warning to interfaith couples. Many rabbis – all Orthodox and Conservative and many Reform and Reconstructionist -- will not perform intermarriages. Even among those who do, their requirements vary -- most will not co-officiate with clergy of other faiths, many require the couple to study Judaism for a period of months and/or commit to keeping a Jewish home and raising a Jewish family. An interfaith couple seeking a rabbi for a wedding often gets a run-around. To avoid this, ask others who have had rabbis who performed interfaith ceremonies whom they used. Alternatively, the board of rabbis often has such information. If you want to understand why rabbis are reluctant to perform intermarriages, read the article on Interfaith Weddings on ritualwell. A final word of caution – while there are independent rabbis and others who will perform interfaith weddings and do a beautiful job, there are some mercenaries out there who will charge an outlandish fee because their services are in demand. Buyer beware.