The old Parktown boy played for Southern Suburbs and Robertsham Callies juniors as a goalkeeper and he was later converted to a defender.

He was regularly selected to play at district levels being coached by former Southampton, Hereford United and Cheltenham Town winger and former Wits University manager Terry Paine.

According to media reports, he was involved in an on-field altercation with a fellow player (goalkeeper Markus Miller) during a German league match in Frankfurt during September 2007.

On 28 March 2017, Carnell was announced as the new assistant coach of the New York Red Bulls of Major League Soccer.

On 5 September 2020, a day after the firing of Chris Armas, he was named interim head coach for the remainder of the 2020 regular season.