A six-person jury convicted Drew Ryser of official oppression, a misdemeanor.
Ryser will serve two years' probation and pay a $1,000 fine as part of an agreement forged between defense attorneys and prosecutors. A jury could have sentenced Ryser to up to a year in jail.
Jonathan Munier, one of the special prosecutors who handled the case, said probation was "fair and just" and he believed the jury would have delivered the same sentence.
"It's not an easy day. It's not a good day," Munier said, referring to authorities having to prosecute a former police officer. "But it's necessary to the system. It's necessary for all of our safety."
Ryser, 32, is the last of four fired and indicted police officers to have their cases resolved in court for their roles in the beating of then-15-year-old Chad Holley.
Holley's beating prompted fierce public criticism of Houston's police department by community activists, who called it an example of police brutality against minorities. Holley is black; Ryser is white.
Defense attorney Lisa Andrews expressed disappointment with the verdict, saying Ryser is "as good a guy as I know."
"Unfortunately, I think he is a victim of a lot of political decisions," Andrews said, declining to say where Ryser is currently employed but saying he would never again consider becoming a police officer. "I feel bad that it's ended this way."
Ryser declined to talk to reporters. Jurors were removed from the courtroom following the verdict and also did not speak to reporters.
Ryser's father-in-law, Jim Smith, said he and other family members were surprised at the verdict.
"Yes, we're very upset," Smith said.
Ryser testified during his trial that his use of physical force against Holley -- including striking the back of his head and hitting him repeatedly with his knee -- was justified because the teenager was resisting arrest and might have had a gun. His attorneys said he followed textbook procedures to arrest a suspect he thought might be armed.
Prosecutors told jurors that Ryser did not follow proper procedures and mistreated a suspect who was not a threat.
In the security camera video of the March 2010 arrest, Holley is seen falling to the ground after trying to hurdle a police squad car. He's then surrounded by at least five officers, some of whom appear to kick and hit his head, abdomen and legs.
Houston Police Chief Charles McClelland Jr. testified against Ryser, saying the video sickened him and gave the department a "black eye."
Two other former officers charged in the case pleaded no contest and were sentenced in April to two years of probation. A fourth ex-officer was acquitted in May 2012. All four officers who were indicted in the case were charged with misdemeanors. Three other officers involved in Holley's arrest were also fired, but two later got their jobs back.
Police said that Holley and three others had tried to run away after burglarizing a home. He was convicted of burglary in juvenile court in October 2010 and placed on probation.
Last year, Holley, now 19, was arrested on another burglary charge, and a judge sentenced him in April to six months in jail and seven years of probation.
A federal lawsuit Holley filed against Ryser, the other fired officers and the city of Houston is pending.
