The 2012 champ, who is currently enjoying an epic comeback four years after his victory on the show, also gave Matt a stern warning.
Matt beat Saara Aalto in this year's final on Sunday night after a shockingly close weekend of voting.
Just 4% split the final three on Saturday evening at the vote freeze when 5 After Midnight left in third place, and at the time Saara was in the lead.
But Matt was out on top come Sunday night and has already released his debut winner's single, When Christmas Comes Around.
As Matt prepares to work on his album over the next month, James advised this year's winner: "Believe in yourself and don't try to be anyone else but you.
"Remain the type of artist that you want to be."
And he warned: "It's easy to get swallowed up by the whole experience, so just try to stay grounded."
Like Matt, James was mentored by Nicole Scherzinger and revealed the pair are still very much in contact four years after he was on the show.
"We speak all the time, we're really good friends," he told Star magazine this week.
Matt's winner's song, written by Ed Sheeran, is available to download and stream now.