Ward, 36, owns Steelers' records with 1,000 receptions, 12,083 receiving yards and 85 receiving touchdowns. The 1,000 catches represent the eighth-best all-time total in the NFL.
He was a third-round pick by Pittsburgh in the 1998 draft and spent his entire career with the Steelers. The team released him last month.
"Today, I'm officially retiring as a Pittsburgh Steeler," Ward said at a news conference. "As much as I'll miss football, my teammates, coaches and everything about the game, I don't want to play in any other uniform. I will remain a Steeler for life."
He helped Pittsburgh to championships in Super Bowl XL and Super Bowl XLIII. He was voted the most valuable player in Super Bowl XL when he had five receptions for 123 yards and a touchdown in a 21-20 win over the Seattle Seahawks.