Fielder had been rumored to be going many places, but has decided on Detroit.
The nine-year, $214 million deal will put him in a lineup alongside Miguel Cabrera.
Both Cabrera and Fielder are first basemen. Cabrera might move back to third base where he has played in the past.
The Detroit Tigers will have a dominant team this year, especially with Fielder's contributions.
He played every game last year, while hitting .299 with 38 home runs and 120 RBI's.