Dr Charles Leale was in close proximity to Lincoln when the President was shot by John Wilkes Booth at a theatre in Washington DC on April 14, 1865.
Released by a researcher, the notes shed new light on a key moment in US history.
Dr Leale wrote: “When I reached the President he was in a state of general paralysis, his eyes were closed and he was in a profoundly comatose condition, while his breathing was intermittent.”
He added: “I placed my finger on his right radial pulse but could perceive no movement of the artery.”
Lincoln is perhaps best known for ordering millions of slaves to be freed during the American Civil War.
The doctor remained with Lincoln until his death. He wrote: “Immediately after death had taken place, we all bowed and the Rev. Dr Gurley supplicated to God on behalf of the bereaved family and our afflicted country.”