Andrew Gallo, 23, held white rosary beads and occasionally looked up at jurors as they returned convictions on three counts of second-degree murder and single counts of drunken driving, hit-and-run driving, and and driving under the influence of alcohol and causing great bodily injury.
Gallo was led away in handcuffs and briefly looked over his shoulder at the victims' sobbing relatives.
Gallo faces 50 years to life in state prison at his scheduled sentencing on Dec. 10.
"I think it's tragic," Gallo's attorney Jacqueline Goodman told reporters outside the courtroom. "I think there's been a miscarriage of justice."
Prosecutors were not immediately available for comment.
Adenhart, 22, died just hours after pitching six scoreless innings in his season debut.
Adenhart, Courtney Stewart, 20, and Henry Pearson, 25, died in the. Passenger Jon Wilhite was severely injured when the impact separated his spine from his skull.
Prosecutors had alleged in the two-week trial that Gallo, whose blood-alcohol level was nearly three times the legal limit, spent hours drinking beers and shots with his stepbrother at three different bars before running a red light and T-boning the car driven by Stewart.
Prosecutor Susan Price told jurors during her closing argument that Gallo "carries the entire burden of this crime. Their deaths lie squarely at his feet."
She said he had been repeatedly warned by friends, family and court officials about the dangers of drinking and driving, but his arrogance and need to party prevented him from learning the lesson.
Prosecutors decided to charge Gallo with second-degree murder not the lesser related charge of manslaughter.
Prosecutors said they charged the case as a murder because Gallo had a previous DUI conviction, had specific knowledge of the dangers of drinking and driving from his own experience and signed a court form from the earlier case saying he understood he could be charged with murder if he drove drunk again and killed someone.
To win a murder conviction, prosecutors had to show Gallo acted with implied malice: intentionally drove drunk; acted with a conscious disregard for human life; and knew from his personal experience that he could kill someone.
Gallo's attorney said her client believed his stepbrother was his designated driver and only drove after his stepbrother became too intoxicated and asked him to take the wheel. By that point, Goodman argued, Gallo was too drunk to realize the consequences of driving drunk.
She said the district attorney had overstepped by charging Gallo with murder and urged the jury to consider their verdict carefully.
"There are gradations of culpability in our society. Not every death is a murder and it's the prosecution that has the burden to prove beyond a reasonable doubt," Goodman said.
In a separate ruling, a judge found Gallo guilty of driving on a suspended license.