On April 28, 2013, Brown signed with the Baltimore Ravens as an undrafted free agent following the 2013 NFL Draft. Brown was one of the 2 rookie free agents to make the 2013 53-man opening day roster. Brown made his NFL debut against the Denver Broncos on September 5, 2013. In that game, Brown recorded his first-career reception and his first-career touchdown. In Week 14 of the 2013 season, he caught the game-winning touchdown from quarterback Joe Flacco with 4 seconds remaining in regulation for a 29-26 victory over the Minnesota Vikings; Brown won NFL Rookie of the Week honors for his performance. Brown tied the rookie record for receiving touchdowns in a season for the Baltimore Ravens with seven TD's, achieving that record against the Cincinnati Bengals. Brown became the first rookie in Ravens franchise history to score a TD in each of his first two career games.
2014 season
In the 2014 NFL season the Ravens signed wide receiver Steve Smith Sr, so Brown was demoted to backup wide receiver. Brown started his first-career post-season game against the New England Patriots on January 10, 2015. In Brown's second NFL season he only had 24 receptions for 255 yards with no touchdowns. In the 2014 season, Brown was part of an offense that broke franchise single-season records in yards and points scored.
2015 season
Brown suffered a back injury in a Week 11 win against the St. Louis Rams. Brown was inactive for every game until December 29, 2015, when Brown was placed on injured reserve, ending his season. The injury ended Brown's third season in the NFL with 14 receptions for 112 yards on 30 targets for zero touchdowns.
Denver Broncos
Brown signed a one-year contract with the Denver Broncos on July 27, 2016. On August 4, 2016, Brown was waived due to a back injury he suffered during training camp. He was re-signed by the Broncos on November 21, 2016. He was placed on injured reserve on December 10, 2016. Following the pre-season, on September 2, 2017, Brown was released by the Broncos.
On April 19, 2018, Brown signed with the Chicago Bears. Following the pre-season, he was placed on injured reserve on September 1, 2018 with a concussion. He was released on October 16, 2018.