Jurors found 66-year-old John Green, of Inkerman Street, Plungington, Preston, had smothered his mother, Bernadette, 88, on May 18.
She weighed just six stone, and was suffering necrosis - blackened rotting skin - amid other injuries and ailments.
Green denied killing her and claimed she declined rapidly in the few weeks before her death and contracted a cough after fall.
However, a police probe uncovered vile text messages he had sent to his daughter in which he referred to the elderly woman as a 'stinking corpse' and in another said: 'When will it die?"
He had claimed he was 'blowing off steam'.
Home Office pathologist Alison Armour gave evidence about the injuries on Mrs Green's severely emaciated body, including indentations in her mouth and marks on her face, which indicated smothering.
Dr Armour, who conducted the post mortem examination on June 8, described how necrosis - blackened rotting skin - was found in intimate areas of her body, and revealed various parts of her body were caked in her own faeces.
Green had told his daughter medics 'could not do anything' for 88-year-old Bernadette Green - but admits he did not inform any medical staff of her problems.
Police enquiries established that despite her deteriorating health, she had not seen a doctor since October 2013 and her son had turned down all opportunities for medical assistance.
The jury was sent out at 3pm yesterday to deliberate the verdict and returned at around noon today.
Green, a divorced father-of-two, was sentenced by the Honorary Recorder of Preston, Judge Mark Brown.
Det Chief Inspector Geoff Hurst of Lancashire’s Force Major Investigation Team said: “Naturally our thoughts are with Mrs Green’s family.
“This is an abhorrent case where a man who should have been caring for his elderly, vulnerable mother instead neglected her and ultimately took her life so he could be free of his perceived burden of caring for her.
“Green denied his involvement throughout despite significant evidence to the contrary and I would like to thank the jury for carefully considering all the evidence and arriving at this decision.
“We welcome his conviction and hope it brings some justice to Mrs Green’s family and friends.”
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