The induction ceremony is in August at Canton, Ohio.
Seau, elected posthumously, was the only first-time eligible candidate to get in this year. He committed suicide at age 43 in 2012, and researchers who studied his brain said it showed signs of chronic traumatic encephalopathy, a disease connected to repeated head injuries, including concussions.
His death, less than 2 1/2 years after the end of his playing career, resonated among players in the league, raising worry about the physical and emotional toll the sport takes.
Two sons of Seau's represented him on stage with the other seven men elected Saturday when the class was announced during the NFL Honors show.
A field-covering, hard-hitting linebacker, the charismatic Seau played in the NFL for 20 seasons, the first 13 with the San Diego Chargers, followed by three with Miami and four with New England. He was Defensive Player of the Year for San Diego in 1992, made six All-Pro teams, and was a member of the league's All-Decade team of the 1990s.
Patriots coach Bill Belichick said this week he "loved" having Seau on his roster.
"I can't imagine having a Professional Football Hall of Fame without Junior Seau in it," said Belichick, whose team plays the Seattle Seahawks in Sunday's Super Bowl.
"I'd say the one word that comes to me when I think about Junior and football is 'passion.' He was a very passionate guy. A lot of energy. Lot of enthusiasm. First guy in the building in the morning — watching film, lifting weights, ready for practice," Belichick said. "Energy before the game, on the sideline, during the game. An emotional player, but a smart player."
Bettis, a finalist for the fifth time, was a burly running back nicknamed The Bus who began a 13-season career by earning Rookie of the Year honors for the Rams. He capped it by winning the 2006 Super Bowl with the Steelers in a game played in his hometown of Detroit.
His 13,662 yards rushing rank fifth in history and he had eight seasons of at least 1,000.
When Brown retired after the 2004 season, he ranked No. 2 in NFL history with 14,934 yards receiving, No. 3 with 1,094 catches, and No. 3 with 100 touchdown catches.
He was the 1987 Heisman Trophy winner at Notre Dame. As a rookie with the Raiders, Brown led the league in kickoff returns, return yards, and average yards per return, and was an All-Pro pick as a kick returner. He earned another All-Pro selection in 1997 at wide receiver.
Haley, elected in his 11th year of eligibility, was a defensive end and linebacker for 12 seasons with the 49ers and Cowboys. After entering the league as a fourth-round draft pick in 1986, he wound up as the first player in NFL history to play on five Super Bowl-winning teams.
He finished his career with 100 1-2 sacks and twice was an All-Pro, once at linebacker and once at defensive end.
Shields was a guard for Kansas City from 1993-2006, never missing a game in his 14 seasons. He was a first-team All-Pro three times, a second-team All-Pro four times, and was a member of the NFL's All-Decade Team of the 2000s.
Polian and Wolf were general managers who built Super Bowl champions. Polian's Bills and Colts teams reached a total of five Super Bowls, with Indianapolis winning the title in 2007. Wolf's Packers won the 1997 Super Bowl, then lost in the NFL championship game a year later.