Brown, voted Pittsburgh's most valuable player by teammates last season, was entering the final season of the three-year contract he signed when he was drafted out of Central Michigan in 2010. He would have been eligible for restricted free agency after this season.
Brown made the Pro Bowl last season after becoming the first player in NFL history with at least 1,000 receiving yards and at least 1,000 return yards (1,062). He finished second on the team to Mike Wallace with 69 receptions for 1,108 yards.
"He has played a major role in our success over the past two years," Steelers general manager Kevin Colbert said, "and we are thrilled he will be a Steeler for many years to come."
Steelers Nation had been eagerly anticipating a long-term extension for one of its young receivers, but it was expected to have been Wallace. The late-day announcement of Brown's deal came as a surprise Friday, less than two hours after the Steelers wrapped up their second day of practice.
A restricted free agent unhappy with the $2.7 million tender the team extended for this season, Wallace did not report to St. Vincent College with the rest of his teammates on Wednesday.
Talks between the team and Wallace have broken off, and the Steelers don't plan to talk contract until the wide receiver reports to camp, a source told ESPN.com senior writer John Clayton on Wednesday.
"I'm looking forward for him to be here, get all hands on deck," Brown said Wednesday, "and get everybody moving in the right direction so we can embark on what we can embark on."
Brown said he speaks with Wallace regularly, but that he has not been pressuring him to report and join his teammates.
"We talk about personal things, but his business is his business," Brown said Thursday. "I'm pretty sure he'll take care of it, and when he gets here, we'll embrace him."
Brown's deal could affect Wallace's ability to cash in. The Steelers are up against the salary cap and -- with the exception of Hines Ward -- have been historically averse to giving big contracts to wide receivers. Two years ago, when Brown and Emmanuel Sanders were rookies, Wallace dubbed the threesome the "Young Money Crew."
Brown beat Wallace in the race to cash.
The first time Brown touched the ball in an NFL regular season game, he returned the opening kickoff for a touchdown at Tennessee on Sept. 19, 2010. He only dressed for nine regular season games as a rookie, catching 16 passes. The kickoff return was his lone touchdown, while Wallace enjoyed a breakout campaign of 1,257 yards and 10 touchdowns.
But Brown began to emerge during the playoffs, catching three passes for 75 yards in a divisional round win over Baltimore. His 58-yard reception in the final two minutes -- one he secured by holding the ball up against his helmet -- set up the winning touchdown.
Brown entered last season as Pittsburgh's No. 4 receiver but became quarterback Ben Roethlisberger's go-to guy over the second half. Brown had 51 catches for 846 yards over the final 10 games of the season.
"Definitely, I can get better," Brown said at the end of last season. "I continue to get stronger."
Brown will meet the media to discuss the new deal on Saturday.
Information from ESPN's John Clayton and The Associated Press was used in this report.