The 27-year-old singer is set to wed former World Superbike champion James Toseland - who she has been dating since April 2011 - after he proposed before Christmas, The Sun newspaper reports.
Katie - who was previously in a relationship with Kooks frontman Luke Pritchard - was spotted wearing an engagement ring at Hamburg airport this week.
The `Closest Thing To Crazy` singer and James, 31, were first set up by Katie`s keyboard player Jim Watson last year after he spotted the racing star in the audience of her concert at Sheffield City Hall in Sheffield, North England.
James - who is launching a new career in music after being forced into early retirement following a wrist injury last year - has previously revealed one of the best thing about his new fiancee is that she doesn`t care about his success.
He explained: "Katie has been great. She had no interest in me whatsoever because I was a motorcycle racer. She hadn`t heard of me. She wouldn`t even know what Valentino Rossi looked like.
"It was only because her piano player was such a fan that he kept talking about it on the tour bus after he`d met me. It was nice and a relief for someone so established to be attracted to me because of my personality."