He played college football for the Notre Dame Fighting Irish and was signed by the New England Patriots as an undrafted free agent after the 2010 NFL draft.
Brown attended Proviso East High School in Maywood, Illinois, where he played as a wide receiver and defensive end.
Following high school, he chose to play college football for the University of Notre Dame after receiving scholarship offers from several major Division I programs.
[6] He played wide receiver, safety, quarterback, placekicker, and punter for Proviso alongside future professional basketball player Brian Carlwell.
[9][10] Brown was also a standout track and field athlete; in his senior year, he was a state qualifier in the long jump, achieving a career-best leap of 21 feet, 9 inches and recording a 4.38 second 40-yard dash.
However, following an impressive performance at a Nike combine in Michigan, Brown received offers from several Division I football programs, including Notre Dame, Illinois, Iowa, Nebraska, Minnesota, Northwestern, and Purdue.
[13] Sources: As a true freshman at Notre Dame, Brown played in eleven of twelve games as a substitute strong safety and gunner.
[17] He recorded four solo and three assisted tackles for a total of seven over six games against Georgia Tech, Penn State, Purdue, UCLA, Boston College, and USC.
In his first career start against San Diego State, Brown made a season-high six total tackles and deflected two passes in a 21–13 victory.
[27][28] Following an injury to Jarrad Page and the release of running back Thomas Clayton, Brown was promoted to the 53-man roster and signed a 4-year, $1.82 million contract with the Patriots on October 23.
[33] He made his NFL playoff debut on January 16, 2011, in a 21–28 loss against the New York Jets in the AFC Divisional round, recording one tackle in the contest.
[40] The Colts claimed Brown off waivers on September 2, 2012, where he would play as a gunner and backup safety to fellow Notre Dame alum Tom Zbikowski.
[47] In the 2013 preseason, Brown incurred a hamstring injury during practice; he was later cleared to play in the Colts' season opener against the Oakland Raiders on September 8.
[70] On September 16, 2023, police in Maywood, Illinois launched a search after family members expressed concern at not being able to reach Brown or his mother, Myrtle Simmons-Brown.
[71] Officers discovered the body of Simmons-Brown near a creek behind her home; the Cook County Medical Examiner ruled the death as a homicide caused by blunt force trauma.
[73] Three days later, Brown appeared in an Instagram video tagged in Mexico, in which he claimed that he believed his mother was "on vacation in Sinaloa" and alleged that he had been kidnapped by the FBI.
[73][74] Other videos posted to the same Instagram account showed Brown repeatedly dismissing reports of his mother's death as fake news and ridiculing claims of his disappearance by referencing the film Finding Nemo.
[75][76] On October 7, Brown was detained by Mexican authorities in Mexico City, where he was found in possession of several of his mother's belongings, including her credit cards and cell phone.