Adam Schefter of ESPN first reported the deal.
Moncrief should help form a new pass-catching trio with second-year wideout James Washington, who snagged 16 passes for 217 yards and a touchdown in limited action.
He obviously won't replace Brown, a seven-time Pro Bowler and four-time All-Pro who has averaged 114 receptions per season since 2013.
The Steelers' new pass-catcher also hasn't been that consistent of late, as he has amassed no better than a 55.3 percent catch rate since 2016.
But Moncrief has also faced some obstacles over the past three years. In 2016, he suffered shoulder and hamstring issues and missed seven games. He still caught seven touchdown passes.
In 2017, Moncrief suffered injuries again and missed four games, but he was also without starting quarterback Andrew Luck, who sat the entire year recovering from shoulder surgery.
Moncrief then moved to Jacksonville, where the bottom fell out after a promising 2017 season. The 2018 team scored the second-fewest points in the league, and Jacksonville benched starting quarterback Blake Bortles twice. Running back Leonard Fournette also missed half the season with hamstring injuries, and no tight end accumulated more than 214 yards.
The whole offense was a disappointment, and Moncrief may have fallen victim to that.
But now he's on a stout Steelers offense with a great offensive line, a bona fide star in Smith-Schuster and a solid franchise quarterback in Ben Roethlisberger. Moncrief isn't about to snag 100-plus passes like Brown, but he could see a strong production spike in 2019.