The 24-year-old actress-and-fashion designer - who split from artist Nate Lowman in February 2010 after a two-year relationship - was spotted on a date with Upper Echelon Shoes co-founder Seth Campbell at Lavo restaurant and nightclub in New York.
A source told Us Weekly magazine: "Their relationship is fairly new. They`ve been able to have a few dates on the down low. He`s a downtown kind of guy, likes to party every now and then.
"His company is in the press but he`s not, so it works out that way. They`re both like each other and are just seeing where things go. Having fun."
The couple have also enjoyed numerous other dates in New York, including a night out with Mary-Kate-s actress sister Elizabeth at The Jane hotel to celebrate her 22nd birthday.
Before embarking on a relationship with previous boyfriend Nate in 2008, Mary-Kate was linked to a string of men - including the late actor Heath Ledger - but had been officially single since 2005 when she split from Greek shipping heir Stavros Niarchos.
`Beastly` star Mary-Kate shot to fame alongside twin sister Ashley in hit US TV show `Full House` aged nine months.