The deal is worth $52 million and includes $1 million per year in incentives and $27 million in guarantees, according to ESPN's Adam Schefter.
"Alshon has been a tremendous addition to this organization on and off the field," the Eagles said in a statement. "We place a priority on making sure we are able to build the team around quality players like Alshon who embrace this team and this city the way he has. We are excited about his future here."
The 27-year-old Jeffery came to Philadelphia as a free agent this offseason, signing a one-year deal with the Eagles. He has been a key target for quarterback Carson Wentz.
"First of all I just want to thank (owner) Jeffrey Lurie and the entire Eagles organization," Jeffery said in a statement. "Like I said the other day, I love it here. I'm blessed to have the opportunity to play for this organization and for these fans. Everyone has welcomed me with open arms and now I'm looking forward to being here for a long time. We have a great group here and I'm excited to be a part of it."
In 11 games this season, Jeffery ranks second on the team in receptions (43) and receiving yards (619). He has seven touchdowns, five of which have come in the last four games. Jeffery ranks 16th in the NFL in receiving yards and is tied for fifth in touchdowns.
The 10-1 Eagles have the best record in the NFL heading Sunday night's game at the Seattle Seahawks.
Originally selected by the Chicago Bears in the second round (45th overall) of the 2012 NFL Draft, the 6-foot-3, 218-pound Jeffery has 347 career receptions for 5,168 yards and 33 touchdowns in 74 games. The 2014 Pro Bowl wideout ranks eighth in the NFL with 4,801 receiving yards since 2013.