The person spoke on the condition of anonymity because the Lightning had not announced the deal Friday, the first day of the NHL's free agency period. ESPN.com first reported the agreement.
The Lightning did announce that they've signed rookie first-round pick Jonathan Drouin to a three-year, entry-level contact. Drouin was the third pick in the draft last weekend.
Filppula has shown flashes of promise during his previous eight seasons with Detroit. After scoring 23 goals and finishing with 66 points in 81 games two years ago, he managed just nine goals and 17 points in 41 games last season.