Nix was born in Carbon Hill, Alabama where he later attended Talladega High School and played linebacker. Nix attended Livingston University (now the University of West Alabama) in Livingston, Alabama, playing fullback on their football team.
Nix was head coach at Eufaula High School in Eufaula, Alabama, leading the Tigers to their first Border Conference championship in 1966.
Nix had a successful college football coaching career with the Chattanooga Mocs at the University of Tennessee at Chattanooga. Nix was responsible for recruiting star wide receiver Terrell Owens.
Nix was a regional scout under John Butler from 1993 to 2000 for the Buffalo Bills, specializing in the Southeastern United States.
Nix left Buffalo with John Butler and A. J. Smith after the 2000 season. He was initially the Director of Pro Player Personnel (2000–2001), but after Butler died, Smith was promoted to General Manager, and Nix to Assistant General Manager.
Nix's job with the San Diego Chargers was to oversee both professional and college scouting and to be one of the main decision makers in each NFL Draft. Nix was a major reason the Chargers turned around from a losing football team to a rebuilt, winning team. In 2004, three players Nix drafted were selected to the 2005 Pro Bowl. In 2005, six players Nix drafted were selected to the 2006 Pro Bowl. In 2006, eleven players Nix drafted were selected to the 2007 Pro Bowl. In 2007, eight players Nix drafted were selected to the 2008 Pro Bowl.
The Chargers won four of the last five AFC West titles with Nix as Assistant GM and Director of Player Personnel, in charge of college scouting and instrumental to the decision making process of their NFL drafts.
Nix was hired as a National Scout for the Buffalo Bills on January 26, 2009. He was named General Manager of the Buffalo Bills on December 31, 2009, after Russ Brandon was promoted to CEO.
He extended the contract of running back Fred Jackson before Jackson was allowed to hit free agency. He also extended quarterback Ryan Fitzpatrick's contract. This cleared the way for him to work to re-sign wide receiver Stevie Johnson once he hit free agency and then work to improve his defense by adding Mario Williams.
On May 13, 2013 the Bills announced that Nix will step away from his role as GM and transition to Special Assistant.
It has been reported by numerous media outlets that Nix would not be returning as Special Assistant after the conclusion of the 2014 season.
Nix has three children: Steve (wife: Sherry) and Stan (wife: Holli), and Stacey (husband: Alan). Nix also has six grandchildren: Hope, Ana, Tyler, Dakota, Sawyer and Tucker, and he has three step-grandchildren: Macaela, Haydn, and Jake.
His wife is Diann Abernathy of Lafayette, Alabama.