After a trial in New York, the jury found Majors, known for playing Kang in the Marvel universe, attacked British choreographer Grace Jabbari during an altercation in March.
She told the court she was left with a fractured finger, bruising, a cut behind her ear and “excruciating” pain.
Majors now faces up to a year in jail.
A sentencing hearing will be held in February 2024.
The six-person jury’s verdict was announced on Monday, Dec. 18 following three days of deliberations.
The assault took place when the couple were in a car in New York and Jabbari saw a text message from another woman on Majors’ phone, which said: “Wish I was kissing you right now.”
According to prosecutors, when she took the phone, he then grabbed her, twisted her arm behind her back and hit her in the head to get it back.
“I felt like a hard blow across my head,” Jabbari testified.
The jury found him guilty of two of the four domestic violence charges that he was facing.
He was found guilty of assault by recklessly causing physical injury, as well as harassment.
But the jury declined to convict him on charges of aggravated harassment and assault with intent to cause physical harm.
The prosecution said the assault was the latest escalation in Majors’ attempts to “exert control” over his girlfriend through physical and emotional violence.
They shared voice recordings and text messages between the former couple with the jury.
“I’m a monster. A horrible man. Not capable of love,” the actor sent in September 2022 while threatening to kill himself.
In audio from an argument that same month, Majors told Jabbari that she needed to act more like Coretta Scott King and Michelle Obama, the wives of Martin Luther King and former President Barack Obama.
“I am doing great things, not just for me but for my culture and the world,” he said, adding that she would need to “make sacrifices” for him.
Lawyer for Majors, 34, claimed the actor was the victim, however, and that Ms Jabbari assaulted him in a jealous rage after seeing the text message in the car.