Williams and his actress wife Ayda Field became parents for the first time last month with the arrival of Theodora Rose.
He said becoming a father was "unexplainable" but it had made him a better man.
"She came out and I went 'this is all I want to do, this makes sense, I want to be with her, I want to watch her grow, and I want to be daddy'."
In a wide ranging interview ahead of this week's release of his eighth studio album, Williams, who has been teetotal for 12 years, also touched upon his well-documented struggles with substance abuse.
"Unfortunately I'm a textbook addict," he said.
"I will use anything at all possible to change the way I feel."
He said that at his lowest ebb, although he never considered committing suicide, he didn't care whether he lived or died.
"There were moments where I didn't care if it ended (although) I don't think I was going to end it."
But Williams said he was now a very different person.
"I'm very content, I'm loved up, I've got a little girl I need to look after.
"I'm very pleased, honoured and happy to do that."
Williams' new album, Take The Crown, will be released on November 2.