In exchange for the 6-foot-5 pass catcher, the Panthers receive a 2018 third- and seventh-round pick.
For the Panthers, the move is a bit more puzzling, considering Benjamin provided a big target for Cam Newton.
ESPN first reported the move, which came moments before the 4 p.m. ET trade deadline.
The trade sees Benjamin reunited with former Panthers defensive co-ordinator Sean McDermott, who is now Bills coach, and Buffalo's general manager Brandon Beane, who was part of Carolina's front office when the franchise drafted him. Both previously worked for the Panthers before being hired by Buffalo this year.
This trade is hard to process because there are still great unknowns-the greatest of which is the health of Kelvin Benjamin's left knee.
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Bills receivers now rank last in the league in receptions (45) and receiving yards (594). Through eight games this season, he has posted 32 catches, 475 receiving yards and 2 touchdowns.
In his fourth National Football League season, Benjamin was leading the Panthers with 475 yards receiving on 32 catches, with two touchdowns in eight games.
The Bills will have a decision to make on Benjamin's contract for next season as he is owed a guaranteed $8.45-million but can be cut with no dead money.
Suffice it to say, Twitter had some interesting things to say about this trade.
Benjamin, who joined the Panthers as a first-round draft pick (28th overall) from Florida State, has 168 career receptions for 2,424 yards and 18 touchdowns.