It's a one-year deal worth $5 million, and is worth up to $6.5 million with incentives, according to ESPN's Adam Caplan.
Brown spent the first four seasons of his career in Arizona, eclipsing the 1,000-yard barrier in 2015.
The speedy receiver has battled injuries and inconsistency since then, however, catching just 21 passes for 299 yards in 2017.
Brown will join an underwhelming receiver corps in Baltimore, and the team is expected to continue looking to improve the position this offseason.
The 27-year-old's signing could signal the end of free-agent receiver Mike Wallace's tenure with the Ravens.