Pro Football Talk's Mike Florio first reported the sides were nearing an agreement.
The extension does not guarantee Fitzgerald will play in 2018, as he still plans to consider all options, including retirement.
Fitzgerald entered the 2017 season on an expiring deal after he inked a one-year extension in August 2016, but he stated over the summer he wasn't thinking about retiring even though he turned 34 years old shortly before Week 1.
That much has been clear this season.
Despite a rash of injuries that have plagued quarterbacks Carson Palmer and Drew Stanton, Fitzgerald has remained the centerpiece of Arizona's passing attack.
Through nine games, Fitzgerald leads the Cardinals in receptions (60), receiving yards (677) and receiving touchdowns (three). In fact, no other player on the team has eclipsed more than 35 catches or 350 yards.
On a more macro scale, returning for one more season will give Fitzgerald a legitimate chance to move into even more esteemed territory on a pair of the league's receiving leaderboards.
Entering Week 11, Fitzgerald (1,185) sits 140 catches shy of legendary tight end Tony Gonzalez (1,325) on the all-time receptions list. He's also currently sixth on the all-time receiving yards list (15,066)—868 yards shy of Terrell Owens for No. 2 in league history.
However, Fitzgerald has remained adamant that Super Bowl aspirations—not statistical achievements—are why he's sticking around.
"That's the only reason I'm playing at this point," Fitzgerald said of aiming for a Super Bowl, according to ESPN.com's Josh Weinfuss. "From a personal standpoint and the things I've accomplished, they're fine. But the thing that you will say is out of your control because you're in a team sport is a championship."