Liverpool's Aussie winger will receive a percentage of sales after helping develop the newly designed boot.
"In the end it came down to adidas having faith in me from day one when I first started being a regular in the Premier League," added Kewell.
"Probably the biggest plus was being allowed to have an input into the development of the new F50's.
"As they will be marketed under my name in Australia I wanted to make sure the boots were what I considered the best product on the market, and they have come up even better than I imagined.
"A footballer doesn't really have any other tools of the trade apart from the boots, and with the game being so fast and intense, to be able to have boots that give you even a bit more stability and traction gives you an advantage over your opponent.
"I'll take that any time."