Delmas is of Haitian descent. He was born in Delmas, a commune in the Port-au-Prince area in Haiti, on a street named Delmas 25 and moved to Miami, Florida at age 11. When he first arrived he did not speak any English.
Delmas played high school football at North Miami Beach High School in North Miami Beach, Florida.
Delmas played college football at Western Michigan from 2005–2008. The Broncos made the 2008 Texas Bowl in his senior year but lost to Rice 38–14. Delmas was named to the All-MAC Defensive First Team in 2008 and played in the 2009 Senior Bowl All-Star game.
Delmas was considered by some to be a top-10 prospect at his position in the 2009 NFL Draft. Prior to the draft, ESPN's Todd McShay said Delmas had a chance to get drafted in the first three rounds. Delmas was drafted 1st in the second round by the Detroit Lions (33rd overall). Delmas was named 2009 Detroit Lions Rookie of the Year in voting by the Detroit Sports Broadcasters Association.
Delmas was signed by the Lions to a four-year contract. Delmas returned a 65-yard fumble for a touchdown in Week 1 of the 2009 season against the New Orleans Saints. Delmas won September's rookie defensive player of the month award. On December 20, 2009, Delmas became the first rookie in NFL history to record an interception return for a touchdown, a fumble return for a touchdown and a safety in the same season. He is only the second player in NFL history to accomplish the feats in the same season.
Delmas was named a Pro Bowl alternate for the NFC after the 2010 NFL season.
Delmas was named a Pro Bowl alternate for the NFC after the 2011 NFL season, despite missing five games to injuries.
On March 15, 2013, Delmas re-signed with the Lions to a two-year contract worth $9.465 million.
On Sunday October 6, 2013, Lion's Center Dominic Raiola was involved in an incident of trash-talking and hate-speech to members of the UW-Madison marching band. Louis Delmas is credited with both apologizing for his teammate's actions and having a word with Raiola off the field.
Delmas was released on February 13, 2014.
On March 10, 2014, Delmas signed a one-year deal with the Miami Dolphins. The contract is worth a maximum of $3.5 million. He wore number 25, honoring the street name he was born on in Haiti. On December 8, 2014, he was placed on Injured reserve after he tore his right ACL against the Baltimore Ravens.
He was resigned by the Dolphins on March 20, 2015.
KeyGP: games played
COMB: combined tackles
TOTAL: total tackles
AST: assisted tackles
FF: forced fumbles
FR: fumble recoveries
FR YDS: fumble return yards
IR YDS: interception return yards
AVG IR: average interception return
LNG: longest interception return
TD: interceptions returned for touchdown
PD: passes defensed