Terms were not disclosed, but a source told ESPN's Adam Schefter the deal is worth $31 million and includes $23 million guaranteed.
Before the Cardinals announced the agreement, Watt broke the news by sharing a photo on Twitter:
source: me. pic.twitter.com/1Y6okQBUy5— JJ Watt (@JJWatt) March 1, 2021
Watt later indicated he and his wife, Kealia, were traveling to Arizona on Cardinals owner Michael Bidwill's plane. He tweeted two photos, one of himself posing with Bidwill and the other of himself and his wife sitting in Bidwill's plane.
"I'm excited to get started," Watt said on the tarmac after the plane landed. "Very excited to get started, get to work, get to know the people of Arizona."
Four days later, Watt's former Texans teammate and current Cardinals wide receiver DeAndre Hopkins posted on Instagram a photo of himself and Watt edited to be in a Cardinals uniform with the caption: "Let's finish what we started..."
Hopkins reacted to Monday's news by tweeting: "Life is good in Arizona!"
Watt will reunite with Vance Joseph, the Cardinals' defensive coordinator, who was the Texans' defensive backs coach during Watt's first three seasons in Houston.
In Arizona, Watt will be paired with fellow pass-rusher Chandler Jones, who leads the NFL in sacks since he was drafted in the first round in 2012 with 97. Second during that span is Watt with 95.5.
Watt's addition meant minimal changes to the Cardinals' odds for the 2021 season from Caesars Sportsbook by William Hill. Their odds to win the Super Bowl remain 40-1 and to win the NFC remain 20-1. Arizona's odds to win the NFC West moved from 7-1 to 6-1, still the longest odds of the four teams in the division.
"The one thing I can promise you is I'm going to work my ass off every single day to make you proud," Watt said. "Very proud to be a part of the 'Bird Gang' and the 'Red Sea.'"
In 2020, Watt ranked 15th out of 119 qualified pass-rushers in pass rush win rate, according to ESPN Stats & Information research. He finished the season with five sacks, two forced fumbles and an interception he returned for a touchdown. He has been plagued with injuries recently, having played 16 games in a season only twice since 2015.
After the Texans drafted Watt with the No. 11 pick in 2011, he became the face of the franchise, winning three NFL Defensive Player of the Year awards from 2012 to '15. Watt is one of three players to win that award three times.
A five-time Pro Bowl selection and five-time first-team All-Pro, Watt was by far the most productive pass-rusher in Texans history with 101 career sacks.
ESPN's Sarah Barshop contributed to this report.