He accepted an athletic scholarship to attend the University of Texas at Austin, and played for the Texas Longhorns football team from 1993 to 1996. As a senior in 1996, he was recognized as a consensus first-team All-American.
The Denver Broncos selected Neil in the third round (67th pick overall) of the 1997 NFL Draft, and he played for the Broncos from 1997 to 2004. After seeing limited playing time as a rookie in 1997, he became a reliable starter on the Broncos' offensive line, starting in 104 of 108 games over the next seven seasons. He played on the Broncos' NFL championship teams in Super Bowl XXXII and XXXIII.
In 2010, Neil was the Republican nominee for the 48th District of the Texas House of Representatives. His opponents were Democratic incumbent Donna Howard and Libertarian Ben Easton. The election returns showed Howard winning by 16 votes. Neil challenged the results in the Texas House. A select investigating committee found Howard had won by only four votes but that Neil had not met the burden of proof required to overturn the election. Neil dropped the challenge on March 18, 2011, nearly halfway into the legislative session.
Prior to pursuing political aspirations, Neil co-hosted "The Morning Rush" with Erin Hogan in Austin's ESPN Radio affiliate, 104.9 The Horn.
Neil's son David played varsity football at Westlake High School in West Lake Hills, TX from 2015 into the 2018-2019 season.