The court was told he felt “shame, guilt and profound regret” for what he had done and that he had left the family home.
“Your mental health issues do no reduce your culpability,” said the judge, the Recorder of Cardiff Tracey Lloyd-Clarke.
She also said there were a number of aggravating factors including the age of the children.
The fact that he had assisted others on how to find such images had “added to the suffering these children were already experiencing for his own sexual gratification”.
Hill will serve half his sentence in prison and half on licence.
He was also made subject of a Sexual Harm Prevention Order which will be in force for 15 years.
Well-known in Welsh politics, Hill was heavily involved in two Welsh devolution referendum campaigns.
He was national organiser of the Yes for Wales campaign for the first devolution referendum in 1997, and was campaign director of the Yes campaign in the 2011 vote on giving the assembly law making powers.
Hill was previously managing director at Positif, which provided advice to companies seeking to lobby Welsh politicians.
