Spikes saw limited action in 2006, playing in nine games and recording 15 tackles as the backup to Brandon Siler. He was a member of the Gators' BCS National Championship team which defeated Ohio State. In 2007 Spikes became a starter after Siler was selected in the 2007 NFL Draft. He started all 13 games at middle linebacker recording 131 tackles (81 solo), which was second in the Southeastern Conference. He tied for third in the SEC with 3 fumble recoveries. He also earned first-team All-SEC along with teammate Tim Tebow.
In 2009, Spikes' production fell to 68 tackles (36 solo). In an October 31, 2009 game, Spikes was involved in an incident where he attempted to gouge the eyes of Georgia’s Washaun Ealey. As a result of this, Florida coach Urban Meyer suspended Spikes for the first half of their next game against Vanderbilt. Spikes later announced that he would sit out for the entire game. As a senior team captain, he was one of three finalists for the 2009 Chuck Bednarik Award, a finalist for the 2009 Butkus Award, a first-team All-SEC selection, and a consensus All-American, receiving first-team honors from The Sporting News and the Walter Camp Football Foundation and second-team honors from the Associated Press.
Spikes was drafted by the New England Patriots in the second round (62nd overall) of the 2010 NFL Draft. He signed a four-year contract on July 26, 2010. Spikes quickly became a starter at inside linebacker in the Patriots 3–4 defense, alongside Jerod Mayo. Against Baltimore in Week 6 of his rookie season, Spikes recorded 16 tackles in an overtime Patriots win. Spikes recorded his first career interception in a Week 13 win over the New York Jets on Monday Night Football.
On December 10, 2010, prior to the Patriots' Week 14 game against the Chicago Bears, Spikes was suspended four games (the remainder of the 2010 regular season) for a violation of the NFL's banned substances policy, reportedly for an ingredient in Spikes' ADHD medication. The same day, Spikes released the following statement:
"I’ve been contacted by the NFL and informed that I will be suspended four games for the detection of an illegal substance in a drug test. The substance was a medication that I should have gotten clarification on before taking. It was not a performance enhancer or an illegal drug. The integrity of the game is very important to me. I understand the league’s ruling and apologize to my teammates, the fans and the Patriots organization for this mistake."
He finished his rookie season with 61 tackles, one interception, and three passes defensed. With his season shortened by the suspension, he played in 12 games, starting eight.
Spikes dealt with a knee injury during the season, but played in all 16 games. After being late to practice in January 2014, Spikes was placed on injured reserve. Spikes was not resigned by the team in the offseason.
As a child, Spikes was raised by his brother, Breyron Middlebrooks, while their mother, Sherry Allen, worked 12-hour days at a fiberglass plant. In 2003, Middlebrooks was found guilty of first-degree murder and sentenced to life in prison, the result of a drug deal in 2001. He writes to Spikes regularly and watches what games he can from his cell at Scotland Correctional Institute in Laurinburg, North Carolina. He is the younger cousin of free agent' Takeo Spikes.