Porter got engaged to Bridesmaids star O'Dowd last year and it was later rumoured that they would have ceremonies in the UK and US and have a performance from The Voice UK singer Ruth Brown.
"This 'news' story about our two weddings (eh?) and Ruth Brown singing for us (no) is everywhere," Porter said on Twitter.
"Non of it is true. Dear Papers, shhh now."
She continued: "We love Ruth, but Chris made a flippant comment about that to the press but it was never discussed.
"On the other hand..http://vimeo.com/45418576 @jessicamauboy x x.
"But I still think Ruth Brown should have won The Voice."