Carl Askew, 47, was given a 32-week sentence, suspended for two years, after his tanker crashed into a crane driven by Michael Coleman, 50.
Mr Coleman's partner Wendy Ann Randal told Cardiff Crown Court she did not "bear malice to the driver".
Askew, of Gloucester, admitted causing death by careless driving.
Judge David Wynn Morgan said "it would be a hard hearted court" if it did not take into account the wishes of the victim's partner.
The court heard that Mr Coleman, of Ammanford, Carmarthenshire, had been driving his crane between Junction 32 and 33 on the M4 motorway on 2 November.
The vehicle was restricted to travelling at just 30mph (48km/h) and had been displaying the correct warning lights when the tanker collided with the rear of his vehicle at a speed of up to 56mph (90km/h).
The crane was forced off the road by the impact and overturned on an embankment.
Mr Coleman suffered traumatic head injuries and died at the scene.
Askew told police after the collision that he had sneezed at the moment of impact but could give no explanation as to why he had not seen the crane beforehand.
He said: "Before I could brake, the impact happened."
Mr Coleman's partner of 14 years told the court in a victim impact statement, which the judge described as "astonishing", that the couple had recently been on a holiday together which left her with "wonderful happy memories".
She said: "Since the accident, I feel lost without Mike, he was my everything.
"I know the driver didn't set out to kill Mike. It has left a massive desolation in myself and my children. I do get depressed, but I look at my family, remember and smile."
The court was told that Mr Coleman did not know at the time of his death that his daughter was pregnant and that he was to become a grandfather.
She asked in her statement for the court to consider not imposing an immediate custodial sentence.
In addition to the 32-week prison sentence, suspended for two years, he was disqualified from driving for five years and must carry out 250 hours of community work.
A tanker driver who caused the death of a man in a crash on the M4 has been spared an immediate prison sentence after a plea from the victim's partner.