Guests who could also help the couple celebrate later include Ed Sheeran and Ellie Goulding, model Cara Delevingne and former Made In Chelsea star Millie Mackintosh.
Oprah was wearing a pale pink dress and matching shoes as well as a wide-brimmed hat with a feather and flower embellishment.
They are among 600 celebrities, royalty, athletes and family friends invited to St. George's Chapel, where the wedding will start at noon (1100GMT).
Getty Images Royal Wedding worst dressed Victoria Beckham's dress was navy but looked funeral black on camera
WINDSOR, England Thousands of well-plumed guests and enthusiastic royal fans streamed into Windsor on Saturday, all seeking to capture their piece of the British extravaganza that is the royal wedding of Prince Harry and Meghan Markle.
Closely behind was the one and only Oprah Winfrey who looked wonderful in pastel pink, and appeared to be having a good chat with Idris, before heading off to find her seat.
The legendary Oprah Winfrey is among the few high-end worldwide celebrities invited to witness and celebrate the marriage of prince harry and meghan markle in Great Britain.More news: Unveiled design concept BMW iNEXT
Elton John, who made a beeline for the Beckhams on arrival at the chapel, was twinning with James Blunt in a navy tailcoat, grey waistcoat and powder blue tie.
Markle will be accompanied by her mother, Doria Ragland, when she is driven to the chapel on Saturday, and many of her closest friends and some co-stars from "Suits" will be in the audience.
Singer Joss Stone, actor Tom Hardy and actress Carey Mulligan were also among the guests, as were comedian James Corden and Julia Carey. He sported pink eyeglasses as he arrived with husband David Furnish.More news: Distant galaxy hints at universe's earliest stars
Queen Elizabeth arrived at the chapel with her husband Prince Philip shortly before the ceremony began.
Harry too will be thinking of his late mother Diana, Princess of Wales, who died in vehicle crash when he was 12.
Earl Charles Spencer, who spoke memorably at Diana's funeral on behalf of his family, was seen entering the church.More news: Mac Miller arrested for DUI after hit and run auto crash