Marion Fountain Mortimer, the daughter of Mr. and Mrs. John Jay Mortimer of New York, is to be married tomorrow afternoon to Stephen Wharton Gaghan, the son of Mr. and Mrs. Thomas Hague of Louisville, Ky. Cantor William Humphries will participate in the Episcopalian ceremony at St. Thomas Church in New York.

The bride, 25, is known as Minnie. She received a certificate in visual studies at the International Center of Photography. Her mother, Senga M. Mortimer, is the senior editor at House Beautiful magazine in New York.

The bride is a great-granddaughter of Henry Morgan Tilford, a president of Standard Oil of California from 1893 to1907; she is also a descendant of John Jay, the first chief justice of the United States.

The bridegroom, 42, is the screenwriter and film director. He won an Emmy Award in 1997 for co-writing an episode of “N.Y.P.D. Blue.” In 2000 he wrote “Traffic,” for which he won an Academy Award. He also wrote and directed “Abandon” in 2002 and “Syriana” in 2005.

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The wedding is set for 1:30 PM on Saturday at St. Thomas Church at “Fifth Avenue and 53rd Street” according to the invitation, making a nod at WASP gentry history as the preferred time (and location) for unions. The ceremony is traditional, Episcopalian. There are no bridesmaids; all eyes will be on Minnie, who is being dressed by Oscar de la Renta. The lunch reception will follow at 583 Park Avenue. Afterwards, the couple will honeymoon in St. Barth’s before coming to Los Angeles, where they will primarily reside, and where they also first met- at the annual Oscars picnic of Diane von Fürstenberg.

Some guests at the wedding include Minnie’s best friends Devon Schuster, Lilly Bunn, Kathryn Bohannon, and Dabney Mercer, some of whom are flying in from across Europe today, and also those from her prep school days at St. Mark’s. Others attendees are social relatives like her brother Peter Davis, sister-in-law Tinsley Mortimer, cousin Amanda Burden, and her cousin Averell’s wife Gigi Mortimer. Stephen is bringing in the Hollywood set; Steven Soderbergh, Benjamin Bratt, Michael Douglas, and Catherine Zeta-Jones are all expected to sit on the other side of the aisle.

There hasn’t been this kind of meeting between the Bathing Corporation of Southampton and Hollywood since the days of William and Babe Paley; ironically, Babe was the first wife of Minnie’s uncle Stanley.

Photograph © Style.com.