Around 50 guests are understood to have attended the secret ceremony at Coorabell, near Australia's Byron Bay.
Robbie wore a cream, off-the-shoulder wedding dress, and was reportedly reportedly given away by her mother at the ceremony, held in a tepee-style tent.
Her sister Anya is believed to have been the maid of honour, with brothers Lachlan and Cameron also in attendance.
The pair are believed to have written their own wedding vows.
Cameron was tagged in a photo at what was reportedly their wedding party on Sunday night with four of Margot Robbie's friends.
He wrote on Instagram: "The joys holiday travels; loving families being reunited, gift giving, great food and then..."
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Last week Robbie was awarded the Critics' Choice Award for Best Actress in an Action Movie for her performance as Harley Quinn in Suicide Squad.
She'll be reprising the role in forthcoming spin-off Gotham City Sirens.
This article was originally published by The Telegraph.