Smith, who was released by the Bills with an injury settlement, passed a physical exam and joined the Eagles' practice Tuesday in midsession.
The Eagles released wide receiver B.J. Cunningham to clear a roster spot.
Smith, 29, could be an intriguing fit on coach Chip Kelly's team. He has size (6-foot-2, 213 pounds) and versatility, two qualities prized by Kelly. Smith is the only player in NFL history to score touchdowns on a kickoff return, reception, rush, blocked punt return and pass.
The Eagles are in flux in their return game. Damaris Johnson, who had handled kickoffs and punts, has done neither the past two weeks since injuring his ankle. Although Johnson has been active, Brandon Boykin has returned kicks and DeSean Jackson has returned punts. Smith has returned four kickoffs for touchdowns since 2009.
The Bills signed Smith in 2011 as a free agent after he spent five years with the New York Jets. The plan was to use him as a receiver, return man and Wildcat quarterback. He wound up throwing just two passes and running the ball 34 times in his two seasons with Buffalo.
Smith injured his ribs in the Bills' final preseason game. He was placed on injured reserve and released last week with an injury settlement. That made him a free agent, allowed to play this season for any team except Buffalo.