David Andrew Mapp lobbed the household item at Colleen Wilson during an argument at her home in Tumbi Umbi on the NSW Central Coast on July 28, 2022.
He was found guilty of the 82-year-old's murder by a NSW Supreme Court jury on Thursday.
During his trial, the jury heard Mapp told police he tried to revive his mother for about eight hours before calling triple zero.
After Ms Wilson's death, he pawned her television and whipper snipper for $200, funds he then used to buy heroin.
She was previously forced to pay $700 to get her TV back after her son pawned it.
The 59-year-old claimed he did not intend to kill his mother because at the time he was suffering from severe anxiety and heroin withdrawals, an argument rejected by the jury.
His earlier guilty plea to manslaughter was knocked back by prosecutors.
His defence said he had used heroin since he was 16 years old and relied on his mother for support.
They said at the time of the killing he would have been unable to control his actions as he was suffering from heroin withdrawals and generalised anxiety disorder.
Immediately after murdering his mother, Mapp took 10 Valium tablets.
When emergency services arrived, Ms Wilson was lying on the floor underneath a red blanket with blood and soil surrounding her.
The matter will come before Justice Ian Harrison on February 5, when a date for a sentence hearing will be set.
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