The country singer - who has battled drink and drug addiction in the past - admits the moment he crossed paths with the Oscar-winning actress at a party in 2005 completely turned his life around because it gave him a sense of purpose.
The 'American Idol' judge said: ''I wouldn't say it was a life-changing moment because it was more than that. It was when my life started. That's the only way I can describe it. Meeting Nic was that profound for me.
''Before then I didn't really know what I was doing. Now I know exactly what I'm doing and it all makes sense.
''I feel very, very fortunate that I've met somebody like Nic and we share the same kind of ideology.''
After the couple wed in 2006, Keith, 45, checked into rehab to receive treatment for alcohol abuse and he admits it was Nicole's support that got him through and finally made him kick his habit.
He told the Daily Mirror newspaper: ''We know every part of our relationship because we've built it. Just the two of us. It's beautiful. Nicole listened to her heart and did what she felt was the right thing to do.
''To see that kind of love in action is very moving and deeply inspiring, and just makes me want to be a better man.''
The couple now live in Nashville, Tennessee, with their daughters Sunday Rose, four, and two-year-old Faith.
After having a music career that spanned five decades and saw the release of over...