The 30-year-old, whose second novel, The Luminaries, won the 2013 Man Booker Prize, lives with the poet in Mt Eden.
Toussaint was born in Chicago and emigrated to New Zealand in 2011 after completing an master of fine arts degree at the Iowa Writers' Workshop, where the couple met.
He then started a PhD in creative writing at Victoria University in Wellington.
Catton has kept details of the couple's wedding today quiet.
But in the past, she has spoken about their relationship and how Toussaint is always the first reader of her drafts.
When asked by Scotland's Sunday Herald if they argue if he suggests a rewrite, she replied: "Oh yes. When I killed off a character in The Luminaries, he had lots of critical things to say about how I'd handled it. There were tears on both sides.
"The following morning, I woke up and made the changes he'd suggested because, guess what, he was right."
She added: "But I'm so glad that Steven's a poet. I don't think I could bear to live with anyone who writes fiction. Two novelists in the same house, that would be madness."
