The news of Brown's trade request comes right after the Pro Bowl wide receiver tweeted a farewell to the Steelers and their fans, saying it is "time to move on and forward."
Brown, 30, has been the subject of widespread trade speculation after he failed to show up to work the day before the season finale against the Cincinnati Bengals.
Team president Art Rooney II told reporters last month that something changed with Brown the last week of the season, and he wasn't sure why. He said he had reached out to Brown to no avail.
Agent Drew Rosenhaus told ESPN on Jan. 25 that he had spoken to the Steelers to express Brown's "position" but wouldn't divulge details.
A source close to Brown believes the wideout is tired of playing the scapegoat for the Steelers' problems and wants to show he can thrive in another offense.
Brown is due a $2.5 million roster bonus on March 17. If the Steelers trade him before that date, they would absorb $21.12 million in dead money on their salary cap. That amount would rise to $23.62 million if Brown is traded after March 17.
Brown, who turns 31 on July 10, is due salaries of $12.625 million in 2019, $11.3 million in 2020 and $12.5 million in 2021.
He has no guaranteed money left on his contract. Trading Brown after June 1 would allow the Steelers to spread the cap hit over multiple years, according to ESPN's Dan Graziano -- $9.54 million in 2019 and $14.08 million in 2020.
The Steelers have been prepared for trade scenarios and believe they can get a high draft pick for Brown. One high-ranking AFC executive believes the Steelers will ask for a first-round pick.
Brown has hinted he wants the San Francisco 49ers to make that move. He's used social media to photoshop himself in a 49ers jersey and FaceTimed with 49ers legend Jerry Rice, who last month told 95.7 the Game that Brown "badly" wants to be in San Francisco.
A recent ESPN article highlighted Brown's rocky relationship with the Steelers, who tolerated Brown's antics for years. Brown was routinely late for meetings and games and lived off campus during training camp, multiple teammates said. But largely that wasn't a problem because Brown worked so hard and produced on Sundays.
Then things changed in 2018. Brown became incensed on the sideline in Week 2 against Kansas City. That next week, he tweeted "trade me let's find out" to a former Steelers staffer who wrote that Brown should thank quarterback Ben Roethlisberger for his production. A source said Brown wasn't happy with Roethlisberger's public critiques of his route-running in a Week 12 loss to Denver. And the Week 17 issues confused many with the team.
From the Pro Bowl, several key Steelers publicly supported a Brown return. But now, the Steelers seem resigned to the fate. Asked for a reaction Tuesday, one player said he simply didn't have one anymore.
ESPN's Jeremy Fowler and Field Yates contributed to this report.