Lamas' father is Cuban and his mother is Mexican. The flags of these two countries are often displayed on his clothing during his fights. Lamas graduated with a degree in exercise science from Elmhurst College in 2005, where he was a member of the men's wrestling team and earned All-American honors at the NCAA Division III Men's Wrestling Championships at 157 lbs. During his collegiate wrestling career (2001–2005), he racked up over 100 wins. He was also a two-time CCIW Champion, and was named the CCIW's "Most Outstanding Wrestler" during the 2003-04 season. Lamas returned to Elmhurst after graduation to serve as the assistant men's wrestling coach.

On March 1, 2009, Lamas made his WEC debut at WEC 39 in Corpus Christi, Texas against IFL and WEC veteran Bart Palaszewski. Lamas took the fight with 4 days notice. Lamas controlled Palaszewski with superior wrestling and scored with excellent ground-and-pound to win a unanimous decision over the more experienced fighter. Lamas suffered his first loss via TKO against Danny Castillo at WEC 42 on August 9, 2009.Lamas defeated James Krause via unanimous decision on November 18, 2009 at WEC 44. Lamas then faced Bendy Casimir on March 6, 2010 at WEC 47. He won the fight in stunning fashion by defeating Casimir via flying knee KO in the first round. Lamas defeated Dave Jansen via unanimous decision on August 18, 2010 at WEC 50.Lamas was expected to face Maciej Jewtuszko on December 16, 2010 at WEC 53,but Jewtuszko had to withdraw as he suffered a broken hand during training. Lamas instead, in his last fight at LW, faced current UFC BW Yuri Alcantara and lost via KO in the first round.

In October 2010, World Extreme Cagefighting merged with the Ultimate Fighting Championship. As part of the merger, all WEC fighters were transferred to the UFC. In his UFC debut, Lamas faced returning UFC veteran Matt Grice in his featherweight debut on June 26, 2011 at UFC on Versus 4. Lamas defeated Grice via TKO in the first round. Lamas faced Cub Swanson on November 12, 2011 at UFC on Fox 1. Lamas won via second round submission after applying an arm-triangle choke, earning Submission of the Night honors.Lamas was expected to face Dustin Poirier on February 4, 2012 at UFC 143, replacing an injured Erik Koch. However he then pulled out due to injury.For his third UFC fight at featherweight, Lamas faced Hatsu Hioki on June 22, 2012 at UFC on FX: Maynard vs. Guida. He defeated the heavily favored Hioki via unanimous decision. Lamas was briefly linked to a December 2012 bout with Frankie Edgar, however the pairing was scrapped after Edgar was tabbed as a replacement for the injured Koch to face José Aldo at UFC 153.

Lamas was expected to face Koch on December 29, 2012 at UFC 155, but the fight was postponed until January 26, 2012 at UFC on FOX 6. Lamas was able to control the fight before eventually winning the fight in by TKO (elbows) in the 2nd round. The win would earn him a shot at the belt and he would get his chance to take it away from reigning champ José Aldo at UFC 169. However Aldo had other things in mind and would earn the Unanimous Decision victory.