George Collier was convicted of gross negligence manslaughter at Mold Crown Court in a case brought forward by the Crown Prosecution Service.
Collier had been undertaking work outside a house in Ffordd Penrhwylfa, Meliden in Prestatyn on 26 July 2008 when the incident occurred.
Three-year-old Meg Burgess and her mother, Lindsay Burgess, were walking in front of the wall on a public footpath.
North Wales Police and the Health and Safety Executive (HSE) launched an investigation, which found the wall had only recently been built.
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It was intended as a retaining wall, but had not been designed or built sufficiently for this purpose and subsequently collapsed. The toddler, who was walking behind her mother, was killed.
HSE Inspector Debbie John said: "This was an entirely preventable incident that resulted in the tragic death of an innocent three-year-old girl.
"On the day of the incident George Collier and Parcol Developments Ltd backfilled the wall despite knowing that retaining walls should be designed by a specialist structural engineer. Neither had engaged a structural engineer to design a safe retaining wall."
Rosemary Ainslie, lawyer for the CPS Special Crime division, said: "Mr Collier was responsible for the design and construction of the wall but did not make sure it was built to safe standards, nor did he prevent members of the public from walking past it, with terrible consequences.
George Collier, 49, pleaded not guilty to charges of gross negligence manslaughter December 2011. His company, Parcol Developments pleaded guilty to breaching Section 3 (1) of the Health and Safety at Work Act 1974 at the same time.
(IT/GK)
