Jackson will earn $48.5 million over five seasons, a league source told NFL Network insider Jason La Canfora.
"We are thrilled to be able to keep one of the NFL's top playmakers in Philadelphia," Eagles coach Andy Reid said. "DeSean is a game breaker. He has the speed and ability to score from anywhere on the field, and he has proven himself to be a big threat for our offense."
The Eagles applied the franchise tag to Jackson before the league deadline earlier this month. Had the two sides not worked out an agreement, Jackson would have received approximately $9.4 million in 2012.
According to La Canfora, the Eagles had been reluctant to enter into a long-term contract with the receiver, who is coming off a season in which he totaled just 961 receiving yards and four touchdowns.
Jackson held out last training camp because he wanted an extension. He was deactivated for a game for being late for a team meeting and dropped more passes than usual, and his production dropped. The Eagles are counting on Jackson to be the dynamic player he was during 2009 and 2010.
"Signing our own players was a big priority for us this offseason," Reid said. "And DeSean was certainly high on our list. We are very excited about his future as an Eagle."
Jackson has career totals of 230 receptions, 4,096 yards and 21 touchdowns in four seasons in Philadelphia after he was a second-round pick in 2008 out of Cal. He also has three rushing scores and a franchise-record four punt returns for touchdowns.
Eagles quarterback Michael Vick posted his congratulations to Jackson on Twitter: "Congrats to my Lil brother @DeseanJackson10 your greatest years are still ahead of you bruh. #letswork #birdgang #bleedgreen."
Jackson, 25, was named to the Pro Bowl following the 2009 and 2010 seasons, and is one of five players in NFL history to at least 900 yards receiving in each of his four seasons.
The Associated Press contributed to this report