Dobbins attended Glencliff Comprehensive High School in Nashville, Tennessee and led the Colts to the 1999 TSSAA Class 5A State Champion Runner-Up. He was also picked by the TSWA as a first team All State Linebacker in 2001 which was his senior year. Tim played at Glencliff with some of the most talented players to ever play at the school. During his career, he played with multiple other All State players that went on to have success at the college and professional levels. Those players include current Arena Football star CJ Johnson, who plays for the Georgia Force, former Buffalo Bills DB, Deon Giddens and former starting Tulsa DB CJ Scott.

At Iowa State University, Dobbins earned all Big 12 honors in his senior season. He led the Cyclones to the Houston Bowl in 2005 and to the Independence Bowl in 2004. He played under coach Dan McCarney. He went to Community College at Copiah-Lincoln Community College in 2002-2003. Made all MACJC Team both years.

Dobbins entered the 2007 season as the first linebacker off the bench behind Stephen Cooper and Matt Wilhelm. In the 2007 NFL Draft, A. J. Smith added some more competition to the linebacking corps with the additions of Anthony Waters and Brandon Siler.

Dobbins was included in a trade during the first round of the 2010 NFL Draft that sent him to the Miami Dolphins. After one season in Miami, he was released on August 1, 2011.

On August 6, 2011, Dobbins signed with the Houston Texans.

In week 10 against the Chicago Bears, Dobbins illegally hit Bears quarterback Jay Cutler, giving him a concussion. On November 14, 2012, Dobbins was fined $30,000 for the illegal hit against Cutler.

Dobbins was released by the Texans on October 22, 2013.

Dobbins signed with the Atlanta Falcons on June 18, 2014. He was released after the Falcons claimed Nate Stupar off waivers.

Dobbins signed with the Dallas Cowboys after a season-ending injury to linebacker Justin Durant. He was released on November 11, 2014, to make room on the roster for Josh Brent.