The PZL-104 Wilga 35A light aircraft came down in Northamptonshire after the tow-line for a UK Independence Party advertising banner became wrapped around the tailplane, the report from the Air Accidents Investigation Branch (AAIB) said.
This caused the aircraft's nose to drop, and although the pilot Justin Adams, 45, "maintained some control of the aircraft" he could not prevent it crashing at Hinton-in-the-Hedges Airfield on the morning of 6 May, the report said.
Mr Farage, who was standing - ultimately unsuccessfully - against Commons Speaker John Bercow in the Buckingham constituency, suffered broken ribs, bruised lungs and facial injuries. He was treated at John Radcliffe Hospital in Oxford and said afterwards: "I must be the luckiest man alive."
Mr Adams was also seriously injured and was trapped in the wreckage of the aircraft by a foot until freed by firefighters.
The AAIB said the plane took off from Hinton-in-the Hedges to tow the banner, with Mr Farage in the passenger seat "intending to receive text messages from colleagues on the ground giving locations where the banner could be shown to maximum effect".