"Glad the business side is out of the way," Sanders wrote on Twitter. "Now its back to playing football and bringing number 7 back to Pittsburgh. Love!!! #Steelernation."
The Steelers had until 11:59 p.m. Sunday night to match the offer. If the Steelers didn't match, Pittsburgh would have received a third-round pick from the Patriots.
By keeping Sanders, the Steelers fulfilled the wishes of quarterback Ben Roethlisberger, who was lobbying the team to keep one of his main targets.
Sanders still is eligible to become an unrestricted free agent after the 2013 season.
Sanders, 26, is a quick, athletic receiver who caught a career-high 44 passes in 2012, doubling his production from the previous season.
He received an original-round tender from the Steelers only because of the team's salary-cap restraints this offseason.
Information from ESPN's Ed Werder, ESPN NFL Insider Adam Schefter, ESPNBoston.com's Mike Reiss and The Associated Press was used in this report.