A marriage officiant is a person who officiates at a wedding ceremony.
Marriage officiant is a civil officer who performs acts of marriage, civil union or commitment. Their main responsibility is to receive and witness the consent of the intended spouses and to ensure the legal formalities, and hence the validity of the marriage or civil union, are observed. Unlike wedding and civil union ceremonies, there is no legal filing of paperwork required for commitment ceremonies.
In the United States, Canada and many other countries around the world, a celebrant is a person who performs religious or secular celebrancy services for weddings, funerals, child namings, coming of age ceremonies, and other rituals.
Most Celebrants are ordained clergy, while some are legal officials (usually judges), and others are Officiants empowered by the Humanist Associations around the world.
Celebrants may perform alternative and nontraditional ceremonies in places, and under circumstances where mainstream religious clergy will not. Some Celebrants perform same-sex weddings and commitment ceremonies. Celebrants, also called Officiants, often perform ceremonies in parks, on beaches, on mountains, on boats, on hiking trails, in hotels, in banquet halls, in private homes, and many other places.
Laws in each state of the United States vary about who has the ability to perform wedding ceremonies, but Celebrants or Officiants are usually categorized as "clergy" and have the same rights and responsibilities as ordained clergy. In Canada and in the US States of California, Connecticut, Delaware, Hawaii, Iowa, Maryland, Massachusetts, Maine, Minnesota, New Hampshire, New Jersey, New Mexico, New York, Rhode Island, Vermont and Washington, and the District of Columbia, the only places in North America where same-sex marriages are legalized, Celebrants and Officiants perform many LGBT weddings. As of 2010, Same-sex marriage are also legally performed in seven countries in Europe including Belgium, Iceland, the Netherlands, Norway, Portugal, Spain, Sweden, one country in South America, Argentina, and one country in Africa, South Africa.
In the United States, celebrants are professional ceremony officiants who believe in the power and effectiveness of ceremony and ritual to serve basic needs of society and the individual. They collaborate with their clients to create and perform personalized ceremonies that reflect the client’s beliefs, philosophy of life, and personality, not the celebrant’s. See Celebrant (United States) for more information.
In Scotland, since a June 2005 ruling by the Registrar General, humanist weddings are now legal, providing that they are conducted by an Authorized Celebrant of the Humanist Society of Scotland making Scotland one of only three countries in the world where this is the case. (The other two are the USA and Norway.)
Celebrants differ from Chaplains in that Celebrants serve the unaffiliated public at large, while Chaplains are usually employed by an institution such as a hospital or other health care facility, the military, etc.
In Australia, Celebrants have a slightly different role, as regulated by local and national laws. See Celebrant (Australia) for more information.
In Quaker weddings the couple marry each other with no third party officiating.
In the Catholic Church, it is the bride and bridegroom who perform the Sacrament of Matrimony (marriage), but a marriage can only be valid if the Church has a witness at the wedding ceremony whose function is to question the couple to ensure that they have no obstacle to marriage (such as an un-annulled previous marriage or certain undisclosed facts between the couple) and that they are freely choosing to wed each other.
All ordained clergy (i.e. a deacon, priest, or bishop) may witness the wedding ceremony itself, though usually the wedding ceremony occurs during a Mass, which deacons lack the authority or ability to celebrate; however, in weddings that take place inside Mass, the deacon may still serve as the witness to the wedding, provided that a priest or bishop celebrates the Mass; and in weddings that take place outside Mass (which usually occurs in a marriage between a Catholic and a non-Christian or, less often, non-Catholic), the ceremony is the same for deacons, priests, and bishops (with few or no changes).
Universal Life Church
According to their website  they ordain ministers, priests, men and women worldwide to officiate marriage ceremonies. They believe becoming a Wedding Minister is just the same as a Minister of Faith. The Universal Life Church believes "A vocation is a fruit that ripens in a well cultivated field of mutual love that becomes mutual service, in the context of an authentic ecclesial life. No vocation is born of itself or lives for itself. A vocation flows from the heart of God and blossoms in the good soil of faithful people, in the experience of fraternal love. We are designed with a dreaming brain and a hopeful spirit; it is our nature to envision the life of our dreams. And while dreaming comes easy to us, we must never forget that it takes strength, dedication, and courageous action to bring that dream to life."
The Universal Life Church allows individuals to become a minister, to get ordained or to serve as a wedding officiant. They provide ordination to men and women enabling work in all facets of Christian Ministry in the USA, Canada, UK, Africa, South America, Germany, India, France, Switzerland, Thailand, Japan, Australia, China, Mexico and many other countries throughout the world.
UNIVERSAL LIFE CHURCH, INTERNATIONAL HEADQUARTERS, MODESTO, CALIFORNIA (Not to be confused with the FLORIDA location above)
In existence since 1959, the Universal Life Church is headquartered in Modesto, California, and has congregations around the world. The sun never sets on the Universal Life Church. ULC ministers come from all walks of life and spiritual traditions. Our common thread is our adherence to the universal doctrine of religious freedom:
"Do only that which is right".
Every person has the natural right (and the responsibility) to peacefully determine what is right. We are advocates of religious freedom.
The Universal Life Church wants you to pursue your spiritual beliefs without interference from any outside agency, including government or church authority. 
- Officiant's regulations in Quebec
- Officant's FAQ in California
- FAQ Officiating Weddings throughout the United States, with links to State Code Sections