Dr Freddy Patel was found to be responsible for more than 60 failings while dealing with the case of the newspaper vendor who died after being pushed to the ground by a police officer during the G20 riots in 2009.
Dr Patel concluded that Mr Tomlinson died of coronary artery disease, but an inquest jury ruled that he had been unlawfully killed after additional medical reports suggested a blow to his liver had caused internal bleeding leading to heart attack.
Last month, Simon Harwood, the police officer who pushed 47-year-old Mr Tomlinson to the ground, was cleared of manslaughter by a jury at Southwark Crown Court.
But Dr Patel now faces a hearing arranged by the Medical Practitioners Tribunal Service, on behalf of the General Medical Council to determine whether he is fit to continuing practising as a pathologist.
The panel's findings, released ahead of the hearing, identified a string of failings in two separate reports produced by the pathologist.
The panel found that Dr Patel did not properly consider or comment on the fact that abdominal bleeding found on Mr Tomlinson could have caused his collapse and death.
They also found that the pathologist did not adequately explain how Mr Tomlinson could have died from a heart attack or adequately consider any other possible non-natural causes of his death.
The panel found Dr Patel to be dishonest as he did not identify changes made to his first report referring to Mr Tomlinson's liver injuries, downplaying signs of bleeding by saying there was "no sign of haematoma" on his liver.
He also failed to comment on the significance of these changes, which was misleading, the panel found.
The disciplinary hearing is expected to last three weeks.