The 46-year-old Oscar winner and producer Falchuk, 47, are set to exchange vows this afternoon before 50 family and friends.
A beaming Falchuk arrived at the ceremony in The Hamptons earlier this afternoon.
A source told RadarOnline.com: "Brad pulled up about 10 minutes ago. He was driving himself in a Jeep. He had a huge smile on his face. He looked really happy.
"A few minutes after that, Jerry Seinfeld and his wife pulled up to Gwyneth's house."
And other stars also arrived shortly afterwards.
The source added: "Stephen Spielberg is also there now with his wife, and Joel Madden showed up, but alone.
"Cameron Diaz is understood to be inside Gwyneth's place, helping her get ready."
Earlier in the day workers were spotted putting the finishing touches to the house ahead of the ceremony.
"Lots of workers are showing up at Gwyneth's house to set up her home," added the source.
RadarOnline.com reported how Jerry Seinfeld hosted a party for the couple last night.
Seinfeld and Paltrow are Hamptons neighbors and have been friends for a long-time – her mother Blythe Danner and Robert Downey Jnr. were spotted mingling with guests at the party.
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