The Cardinals had targeted the third-year pro throughout training camp as the next player to get a new deal. A second-round draft pick (47th overall) out of TCU in 2010, Washington led the team in tackles last season with 111.
"I feel really good, really good," he said after practice Thursday. "I'm glad it was able to get done before the season, sooner than later. I feel real good about the decision, about my agent Jordan Woy and the organization. I told them I wanted to be here for a long time and I'm glad it got done."
Terms weren't disclosed, but the deal contains guaranteed money and a pay raise over the next two seasons with a team option bonus in 2014.
Washington, known for his extreme speed at a critical position in Arizona's 3-4 scheme, had 16 tackles for a loss last season, the most by an Arizona player since 1995. He was one of five players in the NFL in 2011 with at least five sacks and two interceptions.
He had two years left on the contract he signed as a rookie.
"It just shows they believe in me, they believe in my talent," Washington said. "It shows the kind of person I am, the kind of character that I have. I'm just excited right now, very excited."
He joins defensive end Calais Campbell as players who signed long-term deals with Arizona in recent months.
"It just shows that they've got two potential great players for a long period of time," Washington said. "We're looking to really take over the defense and really show the organization that we're worth the pay."
He said the contract does not create more pressure for him to prove he's worth it.
"It's more of a challenge," Washington said, "to go out there and play as well as they expect me to play. But I expect that of myself."
Added coach Ken Whisenhunt: "It's great when you have a young player that has made the strides that Daryl has."
"We thought highly of him before we drafted him, and he certainly hasn't let us down, so to know that he's going to be here for a number of years was a great thing."
Washington has plenty of room for improvement.
"I think to continue on that upward scale is the next step for him," Whisenhunt said. "He learned the defense, understood what he had to do in the defense. He's been an explosive player, a fast player. When he knows what he's doing he's hard to block with the speed that he's got. He's all over the place and I think that just getting more and more comfortable in this defense and understanding where he has to be, he can get there fast, and that helps."
The Cardinals had their eye on Washington throughout his college career "on a very good defense" at TCU, the coach said.
"For the fit in what we're trying to get done defensively, he has all the things that you like to see," Whisenhunt said. "He's smart, he's fast, he thumps a lot more than you think he would based on his size (6-foot-2, 230 pounds). He can cover, he can get down the field. All those things to play that linebacker position, a three-down linebacker, make him very valuable.
"Just his work ethic, that's one of the things that you look for in some of these young players, if they're going to be a leader, if they're going to be one of the guys that you count on defensively, they've got to be the right kind of guy, and Daryl is that."
He is among five players from Arizona's 2010 draft class who will start in Sunday's season opener against Seattle.
Campbell was elated to see Washington get the deal.
"He deserved it. He's definitely a great player," Campbell said. "I'd love to play with him a lot of years because he's going to make me look good and make all kinds of plays."
Campbell said the Cardinals were smart to sign Washington now because he would have been a lot more expensive after this season.
"Because he's going to have a great year," Campbell said. "I'm predicting him to be All-Pro."