He joins ESPN as a sportscaster and was to disclose his plans at a news conference in Los Angeles at USC, where he starred in college.
"The opportunity to transition from active player to broadcaster at the level of ESPN and ABC was too great to pass up," Johnson said in a statement issued by ESPN.
Last month, Johnson worked the NFL draft for ESPN, which was impressed enough to offer him a job. He was released by the Carolina Panthers days after the draft.
"When Keyshawn decided to retire from football, we jumped at the chance of adding him to our NFL roster, especially after his impressive on-air performance during the NFL draft," ESPN executive vice president Norby Williamson said. "He delivered passionate opinions and candid analysis, attributes that will make him a first-rate analyst in his new career."
Johnson, who turns 35 in July, spent 11 years in the league. Last season, he became the 16th NFL player with 800 career catches.
He visited the Tennessee Titans last week and met with coaches and watched film.
But the Titans had not made a formal offer, and team officials had been talking with Johnson about the range and money that would be involved in any deal.
Johnson was the top pick in the 1996 draft, by the New York Jets. After a good rookie season - 63 catches, eight touchdowns - for a team that went 1-15, he wrote a book: "Just Give Me The Damn Ball," which was well-received by the public if not by his teammates.
Johnson went on to stints with Tampa Bay, Dallas and Carolina, where he had 70 catches for 815 yards and four touchdowns as the No. 2 receiver behind Steve Smith.
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