The teams swapped seventh-round picks in this year's, with the Eagles moving up five spots to land the 224th selection. The Bills also gave up a conditional draft pick - either a fourth-rounder next year or a third-round selection in 2016.
In landing Brown, the Bills filled a need for depth without having to address it in the draft. He'll serve in a backup role behind co-starters Fred Jackson and C.J. Spiller.
The Eagles, by comparison, had what coach Chip Kelly called ''a logjam'' at running back. Brown was also regarded as expendable in Philadelphia because his side-to-side running style didn't fit Kelly's offense.
Kelly and Bills director of player personnel Jim Monos both said the trade had been in the works for the past month.
Brown has 190 carries for 878 yards and six touchdowns in 32 games in two seasons with the Eagles. He overcame fumbling issues during his rookie season to finish with 564 yards rushing and four touchdowns in 16 games, including four starts.
Brown set the Eagles' single-game rookie rushing record in his first start, when he had 178 yards and two scores against Carolina on Nov. 26, 2012. He followed that up a week later with 169 yards rushing and two scores at Dallas.
In Buffalo, Brown joins an offense that ranked second in yards rushing last season.
''Yeah, I was definitely surprised,'' Brown said. ''But I think it's a great opportunity for me to come in and be able to contribute any way that I can. I'm excited about the journey. And I can't wait to get started.''
This was the latest in a series of trades the Bills have made over the past month.
On Friday, Buffalo dealt receiver Stevie Johnson to San Francisco. Johnson became the odd-man out in a crowded group of receivers after the Bills opened the draft by trading up five spots to select Clemson receiver Sammy Watkins with the No. 4 pick.
Last month, Buffalo gave up a sixth-round draft pick to acquire receiver Mike Williams in a trade with Tampa Bay.
On Friday, the Bills swapped second-round draft picks and picked up an additional fifth-round pick (153rd overall) in a trade with St. Louis.
AP Sports Writer Rob Maaddi in Philadelphia contributed to this report.
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