"I would wake up every morning feeling this more and more of an urge to step out on my own," Timberlake admitted during Sunday's season premiere of Oprah's Master Class on OWN.
But he says he wanted to "try my own hand as a musician, just by myself."
Timberlake, who was just 21 at the time, reveals everyone around him warned him not to leave 'N Sync.
Everyone was thinking: 'Why wouldn't you ride this out? You're the biggest group in the world. Why would you walk away from this'"? Timberlake said.
But he reveals he was set on saying "Bye Bye Bye" and followed his instincts.
"It's one of the best/worst things that I have ever done," Timberlake says.
"It was bittersweet. It was hard to say goodbye to that era, but I felt it changing. I felt music changing. And I felt myself changing."
Justified went on to win two Grammy Awards. By the time his second solo album, FutureSex/LoveSounds, was released in 2006, Timberlake had established himself as a successful solo artist and actor.
But the people around him weren't thrilled about the record's first single, "SexyBack," which Timberlake co-wrote and produced with Timbaland and Nate "Danja" Hills.
"I had to convince people that 'SexyBack' was my song," the singer revealed. "They didn't even think it was me, people thought it was a joke."
"I believed in it and I believed in what it made other people do. You learn to trust your gut. I only have my instinct, which is a powerful thing," he said.
Timberlake, 33, also revealed he originally wrote 'N Sync's hit song "Gone" for Michael Jackson.
But it wasn't until after the group recorded and released the single that the King of Pop decided he wanted to do it as a duet. But by then it was too late.