Both were under agreements that would have expired after the 2012 season, their seventh with Houston. The Houston Chronicle said Kubiak's contract would now end after the 2014 season, while Smith was given a deal through 2016.
Financial terms weren't released.
"I believe it is very important to have stability within an organization and it starts with leadership," Texans owner Bob McNair said in a statement. "We now have all of our key executives and coaches under long-term contracts.
"I feel this action gives us stability going forward and positions us to have many successful seasons for the Houston Texans."
Houston is coming off a 10-6 season in which the Texas won the AFC South and advanced to the second round of the playoffs before losing to Baltimore. The Texans are 47-49 with Kubiak as coach.
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Michael Sam cut from the Dallas Cowboys