The SyCo boss, who has now signed Cardle to his record label, said that the Essex singer's rendition of his Winners' Single 'Many of Horror (When We Collide)' was "the final punch" that sealed his victory.
"He is a worthy winner and when he sang that song the first time around he finally believed he could win," Cowell told The Xtra Factor. "That performance was stunning. He sang it incredibly well and he's a great guy.
"Viewers believed in him, they liked him and he changed it up week-on-week. He also landed the final punch on the night it really mattered.
"You saw the reaction from all the other contestants when he won. All of them apart from one really liked him and you don't see that very often. It meant everything to him and people liked him as a person."
Speaking about his memories of Cardle in the early rounds, he said: "At Boot Camp he was the one where we said, 'where did he come from?' And from then on he put his heart and soul into every week."
He also saluted runner-up Rebecca Ferguson, claiming that she had done Liverpool proud with her efforts on the show.
"I love her and she will have a fantastic career," he said. "She's unique and knows her own mind."