Both operations, which took place in February and August 2013, were committed at the UK's Queen Elizabeth Hospital in Birmingham, the BBC reported. In one of the cases, Bramhall was caught by a fellow surgeon, while the other discovery was made after the patient's liver failed to heal properly and "allowed the marks to be seen."
According to reports, Bramhall used an argon beam to brand both livers. The tool is typically used to stop bleeding or sketch the area of an operation.
"It was an intentional application of unlawful force to a patient whilst anesthetized," Tony Badenoch, one of the prosecutors in the case, said of Bramhall's acts. "His acts in marking the livers of those patients were deliberate and conscious acts."
"This has been a highly unusual and complex case, both within the expert medical testimony served by both sides and in law," Badenoch added. "It is factually, so far as we have been able to establish, without legal precedent in criminal law."
The 53-year-old surgeon, who later resigned from his position after a disciplinary hearing in May 2014, told the BBC outside of court that he had made "a mistake."
Currently free on bail, Bramhall is expected back in court on January 12 for sentencing.
