As a senior, he registered averages of 21 points, 13 rebounds, 5 assists and 4 blocks, contributing to his team reaching the 2004 3A State Tournament semifinals.
Parnell was signed as an undrafted free agent by the New Orleans Saints after the 2009 NFL draft to play defensive end.
[3] On October 14, 2010, the Dallas Cowboys signed Parnell to their active roster with the intention of converting him to a full-time offensive tackle.
That same season after Tyron Smith suffered a high ankle sprain against the Cleveland Browns, he replaced him as the team starting left tackle and also in the next game against the Washington Redskins.
In 2014, he started eight games at right tackle including the playoffs, after Free was sidelined with a foot fracture and an ankle injury.
[6] On March 11, 2015, Parnell signed with the Jacksonville Jaguars as an unrestricted free agent, to become the starter at right tackle and help to upgrade one of the worst offensive lines in the league.