Hamlin was selected by the Seattle Seahawks in the second round of the 2003 NFL draft and also played for the Dallas Cowboys, Baltimore Ravens and Indianapolis Colts.

Hamlin then attended the University of Arkansas where he became the first freshman and only the second defensive back to lead the school in tackles, recording 104 (57 solo).

For his performance, he was named a First-team All-American by The NFL Draft Report and The Sporting News and nominated for the Jim Thorpe Award.

He along with former NFL Players George Wilson and Eddie Jackson were concurrent members of the same chapter of Omega Psi Phi fraternity.

Hamlin entered the National Football League after his junior season at Arkansas where he was considered the Razorbacks best defensive back since Steve Atwater (1985–88).

In his first career start against the New Orleans Saints on September 7, he recorded five tackles and gained national attention after knocking off Donte' Stallworth's helmet on a hit over the middle.

Hamlin was involved in an altercation that allegedly took place between himself and two unidentified men in a Seattle nightclub on October 17, 2005.

[1] According to a police report, Hamlin and his girlfriend were leaving the club at about 2 a.m.,[1] several hours after the Seahawks defeated the Houston Texans.

He was rushed to a local hospital in critical condition with a fractured skull, a small blood clot and bruising of the brain tissue.

In the free agency period of 2007, teams were reluctant to offer Hamlin a multi-year contract because of concerns stemming from his previous head injury.

The next year, he registered 12 starts (missed 4 games with a high ankle injury), 74 tackles and 4 passes defensed.

On September 29, 2010, the Ravens re-signed Hamlin; taking the roster spot of defensive end Trevor Pryce, who was released and subsequently signed with the New York Jets.

On December 22, 2010, Hamlin was signed by the Indianapolis Colts, filling the roster spot made available when Austin Collie was placed on injured reserve.