Nash attended Saint Augustine High School in New Orleans, Louisiana where he played defensive back. He then attended the University of Southwestern Louisiana, where he went from a walk-on defensive back in 1988 to being voted a permanent team captain by 1992.
He is also a former defensive back in the Canadian Football League. After spending training camp with the NFL"s New York Giants in 1993, Nash moved to the Canadian Football League. He first joined the expansion Shreveport Pirates (1994–1995) who folded at the conclusion of the 1995 season. Nash later joined the Montreal Alouettes (1996–1999), but midway through the 1999 season, joined the Winnipeg Blue Bombers (1999–2003) with whom he set a team record for all-time pass knockdowns.
He played his final Canadian Football League season with the Edmonton Eskimos.
In total, Nash recorded 367 tackles and 24 interceptions throughout his Canadian Football League career. He was also named a Canadian Football League All-Star three times.
After retiring from the Canadian Football League after their 2004 season, Nash joined the Patriots as an assistant strength and conditioning coach for their 2005 season. He was promoted to head strength and conditioning coach in 2011.
On January 29, 2016, Nash was hired as the head strength and conditioning coach for the Detroit Lions.
Nash has a son named Harold Nash III.
