The striker, currently without a club after being released by Sheffield United last year, had pleaded guilty to a charge of dangerous driving at Nottingham Crown Court in March.
Sentencing King at the same court today, Recorder Paul Mann QC said: “I do not regard your case as merely impulsive or silly behaviour.
“It was aggressive. It was arrogant.”
The court heard King had been eating an ice cream at the wheel when he caused a three-car pile up on the A46 in Nottinghamshire last April.
The judge also handed King a three-year driving ban.
The court heard that King committed the offence on his 33rd birthday while driving a white 2011 Porsche Panamera.
He was eating an ice cream he had bought from a McDonald’s just moments before the crash, which happened at around 3pm on April 26.
King was seen weaving in and out of traffic before he undertook Martin Beck, whom he perceived as travelling too slowly in the outer lane of the A46, the court heard.
The former footballer slammed on his brakes in frustration, forcing Beck to perform an emergency stop in his black VW Polo.
As Beck came to a halt, another driver in a silver Vauxhall Astra who had pulled out behind him, collided with the stationary Polo.
The “concertina effect” forced the Polo into the back of King’s Porsche.
Mr Beck had to be cut out of his car and airlifted to hospital after the collision at Winthorpe, near Newark. He spent three weeks in hospital and required surgery for a fractured and dislocated forearm.
Mark Bush, who was travelling in the Astra, was also taken to hospital for cuts and bruises.
The court heard that King drove off from the scene but was flagged down by another motorist who feared Beck had been killed by the collision.
King returned to Beck’s car, where he blamed the driver for the collision.
The judge told King: “You were so pumped up with road rage, you had to start accusing him of being to blame for these collisions”.