Frederick Harrington, 78, of Knucklas, Knighton, was suffering from the side effects of strokes, had limited mobility, and was substantially deaf, Merthyr Tydfil Crown Court was told.
But he was let off jail because a judge ruled he would not be able to cope with life behind bars.
Harrington was attempting to parallel park when his foot slipped off the brake pedal and hit the accelerator.
He reversed at speed hitting pedestrian Christine Hughes, 76, who was crushed under his car for an hour.
The “horrific” accident was witnessed by her husband and daughter who were in Knighton, for a family reunion.
Harrington was in the town taking his wife to a hair appointment in the car, which he had bought four weeks earlier.
Prosecutor Robin Rouch said: “Mrs Hughes was knocked down while on the pavement – she went under the revving vehicle.
“Her husband Arthur Hughes and daughter Catherine were doing their best to comfort her. She was in significant pain still trapped under the vehicle.”
Harrington was wearing slippers after attending a clinic for his severe leg problems earlier that day.
He appeared “vacant, confused and disorientated” at the scene and told police his foot slipped off the brake pedal.
Merthyr Tydfil Crown Court heard there was no rubber cover on the pedal making it “extremely slippery”.
Harrington admitted causing death by dangerous driving and was facing up to three years in jail.
But Judge Greg Bull QC ruled he was not capable of coping with prison life because of his “incapacities”.
The judge told him: “You are significantly physically infirm, you have the side effects of strokes, you have limited mobility and you are substantially deaf.
“I have to ask if society finds it necessary to send a man of your age with your incapacities into a prison setting which you would not be able to cope with.”
Harrington was given a two-year jail sentence, suspended for two years.
He was banned from driving for five years and ordered to pay £3,200 court costs.
Judge Bull said: “There can be no more horrible scene for a husband and daughter to see a beloved wife and mother mown down in the way you did to Christine Hughes.
“You were driving a car you had no business driving. You were immobile which created a risk to other road users.
“The brake pedal was to some extent defective in that the rubber cover was missing making it extremely slippery.
“Your foot slipped from the brake onto the accelerator causing you to accelerate at some speed for 25 metres along the pavement.
“I do not think you knew you were on the pavement.”
Harrington, who had no previous driving convictions, surrendered his licence following the fatal accident in July 2019 and the judge ordered that he would never drive again.
Mr Hughes’ victim impact statement said: “I can’t get the details of the terrible accident off my mind – my darling wife was sobbing in pain as she lay crushed beneath the car for over an hour.
“Devastated hardly begins to explain how I feel. It just seemed so cruel and unfair.
“We had built a retirement bungalow, we were so happy, deeply in love and looking forward to spending more time together.
“Life is now desolate and lonely. I miss her every day.”