Sherman announced the deal Wednesday on his Twitter account and on his blog page, saying the extension includes $40 million in guaranteed money.
"The goal has always been to stay in Seattle and continue to play for the Seahawks," he wrote on his blog. "With this chapter closed, I can continue to focus on what is important -- defending our Super Bowl Championship and being the best cornerback in the NFL.
"This is a great moment for my family, foundations and the people who supported me to this point. Hard work and execution got me to this moment, the Seattle Seahawks have backed up that respect with this contract. The terms of my deal are 4 years for a total of $57.4M with $40M guaranteed. There is no other city or team that I would want to play football for."
Sherman also had a quip for the Seahawks' owner.
"I'd like to thank Paul Allen for anteing up," Sherman said.
The two stars on Seattle's Legion of Boom secondary have now both secured long-term deals. Sherman joins free safety Earl Thomas, who became the highest-paid safety in the league last week with a contract extension that will pay him $40 million over four years.
"It was headed in the right direction for several weeks,'' general manager John Schneider said. "I thought it was time to get it tied up and let everybody move forward.''
Sherman insisted getting paid will not change the attitude that took him from being a lower-round draft pick to one of the league's top cornerbacks. He still remembers that 23 other cornerbacks were selected ahead of him in the 2011 draft.
"I don't think you can ever plan this as part of any journey. ... It's one of those things you have to accept and really appreciate and still have the same hunger,'' Sherman said.
Sherman, 26, led the league with eight interceptions last season and was one of the most important contributors to the Seahawks' first Super Bowl championship. His 20 interceptions and 60 passes defensed lead the league since he entered the NFL in 2011 as a fifth-round draft choice out of Stanford.
He gained national attention for his postgame rant on national TV moments after Seattle's victory over San Francisco in the NFC Championship Game. He was called a thug by some, but Sherman transformed the narrative into a talk about racism. He recently was named to Time Magazine's Top 100 Most Influential People.
The Seahawks have done what they said they would do in the offseason by securing the pillars of the defense. Seattle also re-signed free agent defensive end Michael Bennett to a four-year deal worth $28.5 million.
Information from The Associated Press was used in this report.