He said: "The single guys from One Direction are going to have a lot of fun.
"They look great, they sound great and, when you add their British accents into the mix, the American girls are going crazy for them.
"Sure you need the talent, but you need to win over the American public, that's what it is all about. One Direction are genuine good guys.
"The industry needs a fresh boy band, and by the end of this year they will be the biggest boy band in the world."
Justin, 18, revealed he knows a big-name star who has the hots for One Direction's Harry Styles - who is in the group alongside Louis Tomlinson, Liam Payne, Niall Horan and Zayn Malik - but he has been "sworn to secrecy".
He is quoted by the Daily Mirror newspaper as saying: "I already know one of the biggest artists in the world thinks Harry is so hot, but I have been sworn to secrecy."
One Direction scored a number one with their debut album 'Up all Night' last month while touring in the country in support of Big Time Rush.
The boy band will return to the country in December for their biggest headlining concert to date at New York's Madison Square Garden.