Thomas was drafted by the Denver Broncos 22nd overall in the 2010 NFL Draft. He was the first wide receiver taken in the draft over the #1 projected receiver Dez Bryant. Thomas had 8 receptions for 97 yards and scored his first NFL touchdown in his NFL debut in a September 19, 2010 game against the Seattle Seahawks. Thomas battled injuries his rookie season, missing six games.
On February 10, 2011 Thomas tore his achilles tendon while working out and was expected to miss a majority, if not the entirety, of the 2011 season, Thomas was surprisingly activated from the Physically Unable to Perform List on September 3, 2011 prior to the start of the season as Broncos GM Brian Xanders said Thomas had responded to rehab well and was "ready to go."