He played college football for the Oregon Ducks and was selected by the New York Jets in the second round of the 2006 NFL draft.

He was also been a member of the Washington Redskins, Houston Texans, St. Louis Rams, and San Diego / Los Angeles Chargers.

[10] Despite missing remaining three games of the season, Clemens finished 2005 with 2,406 passing yards, 19 touchdowns, four interceptions, and a 152.87 passer efficiency rating.

[12][13] Clemens was selected by the New York Jets in the second round of the 2006 NFL draft, the 49th overall pick, to serve as the secondary quarterback to Chad Pennington.

He made his NFL debut in relief appearance against the Jacksonville Jaguars, recording his first career pass attempt and rushing once for two yards in the 41–0 loss.

A struggling Pennington was pulled by head coach Eric Mangini in the middle of the fourth quarter and replaced by Clemens.

[25] When Mike Nugent, the Jets's kicker, injured his thigh in the September 7 game against the Miami Dolphins, Clemens filled in as the team's placekicker, but was not called upon to kick.

[31][32] On July 27, 2011, Clemens signed a one-year contract with the Washington Redskins where he competed for a backup role during the 2011 preseason.

[34] Clemens was signed by the Houston Texans on November 23, 2011, after starting quarterback Matt Schaub was placed on injured reserve.

[42] After Bradford went down with a season-ending injury in Week 7 in 2013, Clemens started the final nine games, going 4–5 as the Rams' starter and finished with 1,673 yards, eight touchdowns, and seven interceptions.

[55] He is an active and practicing Roman Catholic, and is married with four children with a strong religious devotion to the Holy Family of Nazareth.

Earning International League All Star recognition in 1998[3] Clemens is an active member of Catholic Athletes for Christ.

[58] Clemens also expressed a feeling of deep honour when Pope Benedict XVI blessed and kissed their four-week-old baby girl at the final procession of the Papal Mass on April 17, 2008, at Nationals Park in Washington D.C..[59]